Here is a list of all the postings Clive Foster has made in our forums. Click on a thread name to jump to the thread.
|Thread: What is this fourth (threaded) hole in the die stock holder ?|
Was told that the correct complement of holes is 5. All my decent ones are equipped with the three you normally use with a split die on one side of the handles and two on t'other side at left and right in positions corresponding to the fourth one on the die stock Brian bought. Allegedly this is so that hex die nuts can be held without damage using 4 screws with the fifth, split position, screw backed off and out of the way.
Apparently good quality hex die nuts should have suitable recesses in the sides for the screw points. Not that I've ever seen any so fitted. Come to think of it I don't think I've ever seen anything that might be called a good quality hex die nut. Always assuming there are such things. However several of my dies have recesses for the extra screws. Makes sense with the big pipe dies where some extra drive points are probably useful given that the stock is approaching 2 ft across so the long handles give plenty of leverage. But 5 driving points on a small die seems excessive. Think my 10 BA one has 5 recesses.
|Thread: Help with Choosing a Milling Machine|
If your LUX mill has the same silly screw up and down depth stop that mine had there is a simple and adequately effective fix. I replaced the screw with a solid rod rigidly fixed into the quill collar, drilled out the thread in the Tee nut style traveller and put a wing nut headed screw into the tapped hole that held the indicator plate to clamp onto the vertical rod. On mine the hole for the indicator plate screw went right through into the original thread so I didn't have to deepen the hole. I put a copper disk in before the screw to protect the rod from the clamp screw. I made the wing nut headed screw by simply reducing the diameter of a standard screw head sufficiently for it to screw right down into a standard wing nut. Loctite bearing fit made sure that it stayed there. I found sighting the edge of the tee nut against the scale perfectly acceptable for setting things. Theoretically the screwed system can be set more accurately than simple side but mine wabbled about so much that accuracy was not an appropriate concept and coming down pnto the stop was avery spongey affair.
I got a three axis glass scale DRO for mine. Not Sino but, so far as I'm aware, these glass scales are all of very similar size. Not knowing any better I put my X-Axis scale on the front of the table using alloy blocks maybe an inch (ish) thick. Worked fine but necessitated the replacement of the Bristol style table clamps with plain bolts. I ran a nut tight up against the heads to make it easier to slip a spanner on. Vertical axis went on the quill. Considered putting it on the column with a BW Electronics pull wire sensor on the quill, the digital caliper style scales hadn't really arrived in those days, but decided the extra readout would be guilding the lilly. My Bridgeport now wears a BW pull wire on the quill and a 3 axis Sino system with the vertical on the knee confirming that 4 scales are enough better to be worth the cost.
Besides considering nominal size and machining capability its important to look closely at actual work envelope, accessiblity, visibility and tool change space. Especially if you have been used to industrial size machines. In my view anything much smaller than a Bridgeport is of necessity going to be compromised to a significant degree in those areas as the space and volume requirements to avoid compromise are pretty much fixed and small machines just don't have the physical room.
Dovetail colum machines at least avoid the head location problem endemic to the round column breed where you have to fit tool change room and tool length variations in the quill travel but winding the head up and down can be a pain. I used to have a Chester supplied Lux style machine and rapidly fell out of love with the head lift crank. Power rise and fall is not a luxury on these. The fashionable square, boxy, head assemblies considerably reduce visibility. Its virtually impossible to get a decently downwards look at a milling cutter in operation, indeed with a short cutter nicely snugged up and a desirably short quill extension it can be darn near imossible to see anything at all however unlikely the angle. The base plan dimensions of the Chester LUX head are considerably larger than a Bridgeport J head.
Another unpleasant surprise for the unwary is the limited amount of table area actually covered by the cutter centre. On my LUX variant only about half the Y axis dimension and a little under 2/3 rds of the X dimension could be reached. Which rather took the shine off. Although the limited area covered can be a bit of a pain when actually machining its usually possible to manage the cuts unless the job, realistically, is oversize for the machine. It really bites when it comes to setting up because you are pretty much forced to work below, or at best half to onside, of the head with all the attendant visibility and bits in the way to deal with. No Bridgeport style cranking the table over so you can see and wave your hands around without getting cutter bites. With the smaller machines I'd seriously consider whether a miniature CCD / CMOS video camera would help see WTHIGO.
These and similar issues are best dealt with by physically viewing the machine and doing some serious handle twiddling whilst waving a tape measure around. Don't overlook the vice issue unless you plan to do all your jobs on the table or tooling plates. A vice large enough to hold jobs approaching machine capacity may well be too big to sensibly fit whilst one that fits easily may be too small to do your jobs. Same applies to rotary tables. Note that space needed for job clamping is pretty much fixed so smaller 4" and 6" tables are disporportionately smaller in useful area than larger ones. Another nasty surprise for me despite buying an 8" one, a 10" or 12" seems so mch larger in practice.
I found "grid of tapped holes" plates, mine were Thor Labs aluminium breadboards, much better than Tee slots for much work holding on the LUX style machine and the smaller BCA style machine which preceeded it.
|Thread: Donkey (Mechanical saw to everyone else)|
Although you can get away without a damper on these small hacksaw machines if you only cut solid material of a certain range of sizes, probably covering a couple of inches, around the sweet spot where downforce weight and blade tip co-operate to give best cutting you will run into trouble with tubes and material significantly outside that range. With the aforementioned departmental Kennedy the usual sign that it needed a dashpot top up and, probably, a quick survice was a blade jam or breakage when cutting thin material. Usually the speedframe 1" square tube construction system which we used a lot of. Correct setting of the damper also made a big difference as to squareness of cut. For solid bar, especially at the larger end of the machines capacity, minimal damping was needed for a reasonable rate of cut. In thin materials and speedframe minimal damping resulted in a very unsquare cut but with the damping set appropriately a decently square end was produced.
Ordinary hacksaw blades aren't really stiff enough for power machines. Best blades we found were Keranous(?) Progressive Teeth type which could be got in a thicker (double?) than normal version as well as standard type. The extra stiffness gave noticably better results and the progressive teeth faster cutting. Gawd knows when the stash was got but when it was gone replacement proved impossible as the firm had disappeared. The dashpot also seems to reduce the pressure on the blade during the return stroke leading to longer life.
The Axminster style gas spring to control down force is just plain wrong and needing to add weights plain silly. Its arguable that a machine with a sliding weight on the arm with its position calibrated for different materials, thicknesses et al could be nicely engineered to both work well and be inexpensive to produce but for a firm of Axminsters size to supply a machine that doesn't work out of the box is plain daft.
Our Kennedy never had a cover over the dashpot in my time but I suspect the last few bits dropping into the cavity where what jammed up the dashpot giving me the opportunity to find out what was inside.
Edited By Clive Foster on 27/04/2014 11:53:17
Unlike Johns Axminster device the little Kennedy power hacksaws work just fine with a damper. The Kennedy takes a standard hacksaw blade and is probably around the same effective size as the Blackgates machine.
As I remember things correctly from a quarter of a century (ish) back the Kennedy in the departmental support workshop had a damper dashpot about 2" diameter with a fairly loose fitting "piston" effectively comprising a pair of thick washers with a couple or three large holes drilled in them. The amount of damping was adjustable via an L shaped rod sticking up through the middle which rotated one "washer" with respect to the other so altering the amount of free oil passage through the piston. About 1/3rd of a turn adjustment covering a range sufficient to let the beast cut adequately fast on solid bar yet be reasonably under control when dealing with reasonably thick wall tube. Waterpipe and the like. Very thin wall tube, such as Speedframe, was a bit too much for it. I imagine there was some sort of flap valve included so that the oil didn't get spalshed out when the unsympathetic hoiked the arm up rapidly. There was still noticeable drag when lifting. When the beast was running a certain nodding of the carrier arm could be seen. Probably not enough to indicate actual lift but certainly suggesting a reduction in blade down pressure on the back stroke. Some sort of geometrical magic going on.
Allegedly oil specification is important but ours seemed to work just fine getting a splash of whatever was handy when I noticed things getting low. No one else cared and the place wasn't exactly a regular haunt so for much of the time the oil level would ahve been wrong. Dashpot seems to have been a refinement rather than necessity as the saw still worked pretty well with it near empty. Decent write up on www.lathes.co.uk whith probably enough detail in the pictures for you to scale off.
|Thread: Drill grinding jig design|
Putting aside the fact that many of the cheap import versions are so badly made as to the completely geometrically unsound there is no great difficulty in getting good results from these jigs providing some effort is made to follow the instructions. It does help if you have some understanding of the underlying geometry involved.
These jigs put the drill centre line offset to one side of the pivot axis so a simple side to side sweep brings the drill in front of the pivot by an amount proportional to the sweep angle. This basic movement produces a clearance angle across the drill radius which won't cut unless the angle is so exaggerated as to approximate 4 facet form. To achieve the correct shape where the clearance angle runs around the drill circumference requires the depth of grind to be increased as the swing progresses.
There are two ways of achieving an adequate approximation to the desired geometry with these simple jigs.
One way is to set the pivot stem vertical and the drill cutting edges at an orientation best described with reference to a conventional clock face as 25 past 11. The original Picador jig uses this geometry. The projection is set by lightly butting the lip of the drill against the lip rest. Although it is in some ways advantageous to use the same projection for any given drill size at all point angles the grind accuracy does depend on how closely you manage to set the 25 past 11 cutting edge position. It doesn't help that there are no on jig references. The lip finger fit is usually pretty poor too which merely adds to the difficulty. Especially with small drills.
The alternative method is to set the pivot point at an angle, usually a little under 20°, as in the jig described by Howard Hall whose operation he completely misunderstands. I can only assume Howard did not have the benefit of a proper set of instructions. Here is a link http://www.generaltools.com/assets/i...825_Manual.pdf to one set. The geometric results of the angled pivot plane are essentially similar to the vertical pivot and 25 past 11 drill orientation of the Picador Jig but introduces a component dependant on drill projection distance. This means that you can, in principle, set the drill position by direct measurement where-upon contact between drill and lip rest will produce the right orientation of the cutting lip and heel. Naturally it is a complete pain in the butt to measure the projection of each and every drill prior to sharpening so the carrier trough offset and pivot angle in a correctly made jig are such that setting the cutting edge vertical with the drill in contact with the will work for the common 59° and 68° point angles. For other angles you need different projections.
Although simpler to set-up for normal angles, vertical is much easier to judge than 25 past 11, the angled pivot geometry is not quite as good an approximation as the vertical pivot one. A high heel needing a touch of hand grinding to remove is pretty endemic with larger drills. A slight twist of the drill will, I understand, fix this.
On the Picador jig the drill carrier trough is offset by about 3/16" from the pivot axis. The angled pivot versions I've seen are similar but there is an interaction between pivot angle and offset so there is room for variation.
These devices work much better using a properly dressed cup wheel rather than just rubbing across the side of an ordinary grinding wheel. It's also imperative to provide some means of guiding the base so it remains correctly orientated ay 90° to the grinding wheel face as you slide it back and forth to get the drill to just touch the wheel before grinding. It should be obvious that any twist will completely muller the motion geometry, most especially with the angled pivot version. The vertical pivot is a touch more tolerant but still not very. The simple slot and bolt idea is monumentally inadequate. Its important to judge just the right amount of downwards force on the back of the jig when swinging. The vertical pivot Picador is very sensitive to this. Simply letting things float in the crude vee and plate bearing will not produce consistent results.
The linked instructions from General suggest that the jig can be used on the periphery of the wheel. Something I find hard to believe unless the wheel is very large.
Edited By Clive Foster on 22/04/2014 23:51:39
You certainly can clean up with a suitably profiled boring tool. Don't worry about trying to get the width at the bottom dead right. Concetrate on the flank angles and make the tool come out bit narrow. Set up for 10 tpi with your topslide parallel to the lathe bed so you can adjust the tool to trim one side at a time.
Standard machine tool makers practice back in the day to get minimal backlash nuts. Friend John used to do such for CVA.
|Thread: Mild steel & cast iron|
Simple screw to close up the slit style clamp sounds risky with cast iron onto a square bar. Look to be too many opportunities for monster stress risers leading to cracking if the fit isn't just so. Side screw, with handle if need be, and soft pad against one side of the bar looks to be a safe way.
Alignment can be an issue too. Every simple slide on a square bar thing I've seen has been intrinsically less than precise when it comes to retaining alignment through moving and clamping. Given the choice, on round shafts at least, I like the screw clamped floating collars in a bore at 90° to the shaft system which is strong when clamped and has minimal effect on alignment. If you needed reliable alignment its possible that something similar with simple 45° angles on the collars would work across the corner on the square bar. Take out the corners of the slider so the bar is pushed onto the flats when the screw pulles the collars up together as though it were on a Vee block and it ought to be decently precise.
|Thread: Colchester Student Roundnose Gear Oil|
Mobile DTE24 is ISO 32 viscosity and is sold primarily as a hydraulic oil. Pretty much any premium hydraulic oil with anti-wear additives should be fine. Modern oils are much better than what was around when the machine was made so exact specification is not so important. Anything good and close will do, especially in the home shop where the machine will be relatively lightly used.
Genrally supply issues determine the choice as most of us can't pop down the shop and buy a can off the shelf. I use Castrol Hyspin AWS 32 as my general purpose machine oil and Castrol Magna BD 68 as way / heavy duty bearing oil primarily because RS Components stock them and do reliable, fast, delivery via credit card order at acceptable prices. BD68 is also a wonderful oil-can oil for hinges etc.
|Thread: Imperial fractions on drawings.|
Strictly the common 1/64 and ± 5 thou if no specific instructions are "make it to within" allowances rather than true tolerances. Fine for individually made items and simple enough that we all know what it means in practice but the real thing, as needed when making multitudes of things which have to fit together, usually has to be rather more sophisticated.
As an aside in the classroom I was originally told 10 thou if no instructions which was swiftly corrected to ± 5 when I got back to the shop.
When the drawing office of Mighty Great Big Industries gets involved they need to make sure that the actual dimension and tolerances concerned are unambiguously given and the permitted variation is such that the size variations for mating components don't actually overlap. Its embarrassing when multitudes of holes are too small for the matching shaft to go in.
Where fractions are concerned if a dimension is in 32 nds ± 1/64 takes you midway towards next one up or down so there is the potential for overlap. Taking measurement and calibration errors into account some percentage of components will overlap. When you are close to the middle its easy to estimate wrong way and tempting to do so with a big batch of components close to the (invisible) line! ± 1/128 has a clear gap between the middle of the interval to next 32 nd up or down and the right dimension so overlap is unlikely unless the measuring gear is way out. If you let the statistics guys in on the calibrations they will insist on a 95 % confidence limit that your measuring equipment is within ± 1/4 of the interval so all in all you should be safe and things will fit.
Same principle as a digital instruments least significant digit.
|Thread: Parting off|
Expanding on Jasons advice the parted off piece snaps off when wobble, touching tool, rotation or whatever forces become too great for the tiny piece at the centre to support. Grinding the tool at a slight angle defines which part the main pip is left on. Generally, unless turning far too slowly the small end of the pip snaps near enough flush with the face.
Make sure you are grinding off all the bevel provided on the blade for clamping purposes when sharpening the "top" (for a front mount tool) cutting face. Its easy to get into a minimal grind mindset and slip into not going down quite far enough. Went through a phase of that error a couple of years back and it took me ages to twig why parting off had got finickity. I grind mine flat on top but there is a school of thought advocating a touch of side rake. Back rake to my mind just wastes blade length and promotes tool pull in with front mounting. Not aproblem with the inverted rear mounting you use. Theoretically back rake provides side clearance behind the cutting area but I dont consider the actual clearance enough to make a difference. Especially not if using coolant or cutting oil.
Its a common error, especially for those using smaller lathes, to run too slowly. Hand feeding at slow rpm to keep a nice thin chip which won't bind up is hard.
|Thread: Imperial fractions on drawings.|
Fractions on Model Engineers drawings date back to the days when marking out would have been done with a surface gauge and deep engraved ruler in a vertical holder on whatever surface plate subsitute could be found or afforded. Usually thick plate glass. Clicking a scriber point correctly into the various imperial fractions isn't too difficult, OK a magnifying glass helps for the 64 ths. Actual measurements in 128 ths was always pretty rare although rulers so calibrated were available, I have one somewhere, and more to do with implied tolerancing. It should be immediately obvious that imperial fractions are a named increment digital system so the inherent tolerance is ± 1/4 the increment as being unabiguously closer to the true value than to the next one up or down. So working in 32 nds implies ± 1/128, in 64 ths ± 1/256 and in 128 ths ± 1/512 call it ± 10, 5 and 2 in more familiar thous or ± 0.2, 0.1 and 0.05 in mm. As ever the effects of the errors inherent in practical implementation are a whole 'nother thing.
Surface gauge and rule work to any sort of accuracy with a metric rule is not a pleasant prospect. Far too easy to mis-count.
In these days of relatively affordable measurement equipment its hard to understand the different mindset needed with simpler gear. Heck I have a full sets of micrometers up to 12" and 300 mm, internal and depth micrometers to 8" and 200 mm, verniers out to 2 ft, dial calipers in 6", 8", 150mm and 200 mm, 4 height gauges 2 vernier two Microball. Which, logically, is ridiculous for home shop guy. Probably around £1,000 carefuly spent when right thing at right price came up. Not trivial but people fork out that kind of money for a years golf club subs. There is another £1,000 odd worth out there which we won't mention. Big change from 1974 when it took a deal of hard saving and not a few missed lunches before I could afford my first micrometer, a second hand and somewhat iffy import. When Tubal Cain was writing that sort of equipment level was beyond dreaming for a home shop. Even the local departmental workshops at the MoD establishment I used to work for got along with much less.
Except where you need continuous measurements aligned to the mathematical notation imperial style named increment systems are much more practical out in the real world for jobs which don't need machine precision. If you use the appropriate unit conversion issues are rarely a worry and its usually easy to see if there is a serious error or someone is being silly. How many people who talk of tenth thou precision actually know what a tenth thou really looks like. Decimal point migration can be a major problem with continuous systems. Someone starts talking about 1/10,240 th of an inch increments you start thinking "Hang on a bit ..." and should consider whether another unit is appropriate. But tenth thou goes through on the nod. Flying at 40,000 ft sounds fairly innocuous even to Ms Nervous Flyer. Translate to 7 and 1/2 miles ......
|Thread: Lathe Spindle Clutch|
With a gear head its probably a good idea to have a soft take-up. Easy enough with a mechanical clutch which merely needs an educated hand on the control but if retrofitting an electromagnetic one its most likely better on the motor shaft so the belt provides some drive cushion. Some of the gear head lathes have very short drive belts so maybe re-positioning the motor to give a longer belt run for more cushion should be considered if you do go electro-magnetic.
Car aircon compressor drive clutch from the scrappy looks promising as a relatively inexpensive source for an electro-magnetic clutch. Got one under my bench ready for incorporation into a projectr due for completion in the next month or so.
I've had good results with simple slack belt and spring loaded jockey pulley "clutches" in the past on lathes. My biggest motor was 3/4 HP but such devices are common on petro engined domestic mowers etc so up to a couple or three horsepower should be within capabilities. Nooging around the car multi-Vee serpentine "fan" belt drive repair kits should come up with most of the jockey pulley bits. These days I'd be highly tempted to source a couple of suitble pulleys from a scrap car and change to a multi-Vee belt too.
|Thread: dim tolerances|
Once upon a time, in the days when measuring gear of the standard we now take for granted was both rare and too costly for the individual worker, there was a fairly agreed industrial descriptive terminology for half a dozen or so generally useful fits whether loose, sliding, light press and so on. As Michael says such descriptive terms are in general much clearer to the hobby and occasional machinists than modern terminolgy as they give a pretty clear indication as to purpose from which a fairly good idea of how tight it needs to be can be gleaned. Especially if you have someone to show you physical examples of each although a few examples from common items is nearly as good.
Obviously there is no way to get samples to everyone but it ought to be possible to put some "Model Engineering standard" tolerance numbers to the descriptive fits suitable for "home workshop budget" measurement gear and issue these as a separate resouce. Whether paper or web. I guess an A4 page would be more that enough space to print a short description of the purpose of each fit, tolerances to use and a read across to the modern equivalent term. Back side of the sheet could have a very basic introduction to the proper terminology and a listing of what the normal size of a standard drill, reamer or whatever corresponds to. I suspect the looser end of the scale will need an addition or two to cover the essential slackness that prevents the motion work of a small locomotive from binding up when the suspension moves or going round curves. Rattling good and really rattling good fits maybe.
Naturally anything that didn't fit the standard document would have to be called out specifically by the designer. In practice such such specials are pretty much the only thing called out anyway so in practice there would be no great change. I suspect that such adocument would make life much easier at both designer and builder ends of the job.
Edited By Clive Foster on 27/02/2014 20:29:25
|Thread: New Lathe leveling|
If you can arrange to do so safely it would be prudent to have a look at the underside of the headstock and tail end support castings to see how much contact between lathe and support the maker expects. Generally there will be a small boss around the bolting holes sitting proud of the main casting base which actually contacts the support or bench. Boss diameter of the order of 3 times bolt hole diameter projecting around 1/16", 2 mm or a bit more seems typical judging by the small machines I have seen. It seems that this area is rarely well finished, for example SouthBend 9" machines seem to be left as (nicely) cast, so it may be unwise to assume that the machine will sit with all feet in proper contact on a flat surface. Inspector Meticulous types may suggest that it would be advantageous to set the lathe on a flat surface on large steel washers coated with bodyfiller and allowing to harden before bolting to create a smooth true surface under each foot but this is probably OTT unless the foot surface is unreasonably poor.
In my view all small lathes are made to sit much too close to the bench. Spacing up by 3 inches or so gives room for a proper pull out chip tray and provides space to wield a brush whilst sweeping out the bits that miss the tray. Makes life so much more civilised. My first such tray was the cover off a broken record deck. If you do decide to space it up make proper levelling spacers with adjustment threads. Simple and quick to do, well worth the effort to make the installation job easy.
Odds are that the bench that a small lathe is bolted to will be stiffer than the lathe itself. Not the best of situations if the bench is a live material, such as wood, sitting on a fairly basic floor such as those commonly used with the more affordable variety of shed. The better quality thick chipboard kitchen worktop or, preferably, industrial rated counterparts make a nice dead, thermally stable, bench surface on which to stand a lathe. The finish seems oil proof over a more than a decade too. One of my Southbend 9" lathes sat very happily for over 15 years on such a worktop lightly mounted to a pair of plastic workshop cupboards. At B&Q special clearance offer prices the plastic cupboards seemed worth a try but I did add some judicous stiffening by driving nicely fitted timbers down the hollow molded sections and strutting under the shelves before bolting them in place.
|Thread: Bridgeport Milling Machine feed control module|
I have nice, re-drawn, versions in pdf format which I can send if you PM me with your E-Mail address.
Many thanks are due to fellow forum members John and Ken who kindly supplied me with photo copies of original Erskine data and circuit diagrams just before Christmas which I was able to re-draw and re-dtp into native digital files which print out cleanly.
|Thread: LED snake light and camera|
I bought one of the Lidl units either last time round or time before. Competent unit, excellent value for money and not made so cheap as to be pretty much useless except under ideal condtions. A useful addition to the toolbox but not something I'd spend more on.
The USB laptop accessory devices are still of limited resolution so bigger screen isn't that much of an improvement. Lidl and similar devices are easy to hand hold whilst poking snake into place. Laptop ones need somewhere to stand the laptop close enough to see the screen. None of the jobs I've needed to use mine for could have been done with one of the USB devices. Laptop oop t' ladder or under the Rangie. No thanks. That said a high resolution, VGA or greater, USB accessory camera would be very nice for some jobs. But it needs to be high resolution.
In my view there isn't, in practice, a great deal of overlap in the areas where the two types of device work at least well enough.
Edited By Clive Foster on 24/02/2014 13:04:31
|Thread: Easy Calculation ?|
Although it is neither obigatory or necessary to set the compound slide over for threading the practice does have two not inconsiderable advantages. Especially with smaller machines.
Firstly it avoids handwheel interference between cross and top slide. On smaller machines if both are set parallel for straight in feed things can get very crowded making operation difficult. Indeed some brands actually have physical interference between the handles if the right combination of positions is selected. On larger machines the top slide can interfere with easy reading of the cross slide dial. My Smart and Brown 1024 VSL suffers in this respect, mainly due to the heroic size of the top slide which, like the cross slide, is much larger than usual for a 10 inch swing machine.
Secondly it stiffens things up as the thrust perpendicular to the tool is now divided between the top slide feed screw and the dovetails. If set for straight in feed all this thrust must be taken by the two feed screws. On smaller machines said screws are frequently somewhat slender. Wear and the associated backlash on older machines doesn't help either.
My practice has, for many years, been to use a standard top slide setting of 25°. Works fine for threading both 55° and 60° threads. Probably gets shifted only a couple or three times a year for fast tapers and similar.
Edited By Clive Foster on 08/02/2014 00:10:55
|Thread: Mercer Dial Indicator|
Picture shows the tilting "see-saw" extension device from my Starrett Last Word accessory set used with a standard plunger indicator to pick up an internal taper whent setting the taper turning attachment on my Smart & Brown 1024 VSL lathe. Your Mercer set includes an essentially identical device.
Normally the mounting spigot on the indicator is fitted into the empty hole in the pivoting lever mount with the indicator arranged so the free end of the see-saw pushes the indicator plunger. I could have set things up using the Starrett indicator but it would have obscured the view of the taper somewhat and the spare length of mounting rod projecting through the fixing hole would have reduced the amount of gauging travel. Important in this case because there was a parallel bore around 1/2 inch long before the taper began. The Smart & Brown has plenty of real estate on its massive cross slide to hang things off an old style Eclipse magnetic base as shown which facilitated switching to a tenths thou indicator for final setting up. More rods and clamps involved tho' so much more fiddly.
The rectangular bar and rod are provided to facilitate mounting in a toolpost but can be creatively used in many other ways.
|Thread: Easy Calculation ?|
The easy way is to let the lathe do the maths for you!
1) Assuming the work is already turned to the thread outside diameter bring the tool up to touch the work and set both cross and top slide dials to zero.
2) Move the tool back a touch to clear the work then rack the saddle along until the point is past the end of the work.
3) Feed the cross slide forward past zero by the depth of thread to be cut.
4) Re-set the cross slide dial to zero. The tool point is now at the final depth of cut with both dials readin zero.
5) Pull the top-slide back until it clears the work then move forward to sufficiently to make the first scribe cut to verify that settings are correct.
6) After making scribe cut wind the cross slide back past zero and move saddle back past the end of the work.
7) Re-set cross slide to zero and apply first cut with the topslide.
8) Make first cut and repeat wind back cross slide, move saddle to end of work, set cross- slide back to zero and apply next cut process.
9) Repeat until both dials read zero at the end of the cut and all spring has been worked out. The thread depth will now be what you set in step 3.
If you set the book depth of cut the results will only be correct if the tool tip radius is correct or at least very close to book value. This is rarely the case in a model engineers workshop so it's usually necessary to cut a bit deeper before things screw together. I prefer to apply any extra cuts via the cross slide so when the correct fit has been achieved on either a test piece or the first of several parts I can simply re-set the cross slide zero to match the corrected final depth and all subsequent parts will be correct at zero-zero.
A major advantage of this process over mathermatical calculations it that it works fine for any reasonably sane top slide angle. If calculations are to be correct your set-over angle needs to be closer to correct than is easily achieved with the usual graduations, especially on small machines.
I was taught the method as "zero to zero" also seen it as zero-2-zero and similar variant names can be found by Google search. Geo. H Thomas has also described it both in Model Engineer and in his book "Model Engineers Workshop Manual". I imagine its described in other places. Its so easy and effective that I bemused by it not being the standard textbook way.
Edited By Clive Foster on 06/02/2014 23:00:19
Edited By Clive Foster on 06/02/2014 23:01:17
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