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: Machining a metric external thread|
I presume you don't have a full form 1.5 mm pitch threading tool as this makes the job very easy as you can work direct to standard dimensions. The big problem when using the usual home ground tool is getting the actual in-feed depth just so to cope with the inevitable errors in tip truncation and lathe characteristic induced differences between what the dial says you have fed and what actually gets cut.
Basically you need a way to calibrate these errors out so the actual thread flanks are in the right places.
I'd tackle it by cutting a nice 1.5 mm pitch test piece to fit a decently long hole cleanly tapped with a nice sharp tap. M 10 x 1.5 about 15 to 20 mm deep, including lead in and start bore, should do nicely. Aim for at least 8 quality, full depth threads.
Best way to cut the test piece is with the "zero-2-zero" angular in-feed method as it allows you to directly calibrate the offsets needed to take out any error. To use this method the top-slide is rotated to a little less than the thread flank angle, my top-slide is pretty much permanently set at 25° to do both 55° and 60° threads but arguably 28° is better for 60° ones. Not that I've noticed any difference. After the work-piece OD has been turned to size the tool tip is bought up to touch the work and both thread dials set to zero. Use the cross slide to bring the tip just clear of the work and use the saddle to take the tool past the end of the work. Now feed the cross slide forwards from zero by the depth of the thread you intend to cut and re-set the cross slide dial to zero. Use the top slide to withdraw the tool just clear of the work then thread using the top slide to set the successive cuts and the cross slide to withdraw the tool to return to the start after each cut. Obviously the cross slide is moved back to where the dial reads zero for each cutting pass. When both dials read zero and all spring cuts have been taken the thread cut is what you set up.
Ideally it fits the test piece. In practice it is almost invariably needs an extra cut or two to get a nice fit. Because your nominal depth setting is on the two zero's its easy to add known amounts of extra cut until the fit is right. My practice is to use the cross slide, making the extra cuts by the straight in method, leaving the top slide set on zero. When I get the right fit simply adding the cross slide reading to the original "book" depth gives the correct cut to set-up next time. Alternatively the top slide can be used and a note made as to the new "beyond zero" finishing point, don't attempt to re calculate things so the top slide finish point is shifted back to zero.
Slide locks and good feed stops make life easier but many small lathe feed stops aren't repeatable enough. The SouthBend one being a case in point, 2 or 3 thou variation being common. As ever with the angular in feed method extra thought and care is needed to create clean shoulders and the end of the thread. Best to cut a suitable groove first.
|Thread: Simpler the Better -what do you use?|
Looking at flea-Bay Apple G4 and G5 towers are getting into the chump change bracket so a perfectly adequate CAD only machine could probably be found under £200. Difficult bit seems to be finding a machine with OSX 10.4 and disks or OSX 10.4 Tiger disk set. Seems my 1.25 Dual Quicksilver is only worth about £120 on the open market which is a good reason not to do the Intel jump. If you have a display I'd be tempted to try a mini.
Looks as though Vector have pretty much given up on the mechanical design market as all the Engineer / Mechanical features have (allegedly) been folded into the basic program and no further development is planned. Another good reason not to fork out £1600 on the upgrade.
Never understood why the program makers don't continue to sell a frozen "last version suitable for OS whatever" version at low price on a no support basis. Its no wonder people are tempted to pirate. Vectorworks website explicitly says that versions 11 and below won't run on Leopard and wont be upgraded.
Just noticed your post re TurboCAD as an alternative to VectorWorks. I have both and reckon if you are used to VectorWorks certain aspects of TurboCad will have you inventing new and ever more powerful swear words at ever increasing volume! I imagine CAD programmers are in for a very er "interesting" afterlife.
I bought VectorWorks 10 post redundancy, decided that it was too much hassle to get on with and went back to pushing ClarisDraw to well beyond its design limits. Eventually figuring I really should go to proper CAD I picked up TurboCAD on special offer believing the "its simpler" reputation. I eventually got some sense out of it after a lot of reading on the help forums. Then after TurboCAD Pro V 2.0 IMSI apparently lost the rights to the code base and changed to a completely different system. I got the side-grade-upgrade, TurboCAD Mac Deluxe, which was a buggy as could be with a lot of features gone and pretty much zilch support. Even the forum stalwarts seem to had given up so I bit the bullet about 18 month back and am making a serious effort with VectorWorks. Use-ability doesn't impress me that much, some things are silly hard like hatch and library import / management but progress is being made. The old TurboCAD had an excellent library of useful components but insertion was a complete pain, in comparison VectorWorks handles the insertion very smoothly if what you want is in its standard libraries. Trying to insert a bolt or similar to the right size with TurboCAD is not for the faint hearted.
If you are running an Intel processor Mac it might be best to use the dual boot or virtualisation capability to run Alibre which seems to be generally impressive as a semi-pro intrinsically 3D program in the modern mode. I've yet to dare 3D but it seems hard work in Vector and similar evolved from 2D programs. If you are on an Intel machine and ever decide that you'd like a few shekels back on VectorWorks 11 I would be interested in purchasing it as an upgrade to my V10 as I intend to stay with my Dual G4 Mac until it dies.
|Thread: Harold Hall QTCP, MEW 50, any one using it?|
Armstrong from Armstrong Patent, which they were marketed as for many years. Armstrong invented the beast and took out several patents from around the mid 1890's to mid 1920's. Don't know the specific patented features tho' although the idea of pointing the tool upwards at a generic "little too large" rake angle was clearly important for easy grinding and tool material economy.
The distorted top slide problem is pretty much inevitable on a small lathe with a simple clamp tool holder where all the pull forces go through the stud in the middle. Stiffness depends on thickness and on small machines there just isn't enough room for lots of metal. I suspect 5" or so centre height is about as small as you can go whilst retaining more than satisfactory stiffness. Below that compromise is essential. Obviously a slotted block type holder where all the clamping forces are within the block is better in this respect but obviously tool size is restricted and we are back to the dreaded shim type height adjustment. The conventional QC is even worse it this respect as space for height adjustment can only be found by slimming things a bit more unless the holder proper is made to overhang the slide introducing its own set of problems.
Looking at my picture in a previous post it occurs to me that the bottom plate of a slot type holder could be dispensed with if using Armstrong holders in the configuration shown. A solid trapezoidal pillar, as large as practicable, could be made with two sides angled to match the desired tool holder shank inclinations for turning and facing having two narrow overhanging ledges to carry the clamp screws. The clamping forces should be well enough spread not to distort the slide. Obviously only one holder at a time would be fitted hence some means needs to be devised for sufficiently accurate replacement so there is a certain inconvenience in that respect. Clearly alternative mounts need to be arranged for boring and parting tools but the concept looks promising.
Talking about parting tools I'm amazed that no-one has produced for sale or as a DIY design a solid block with grooves and clamps to carry either the standard parting HSS blade or the modern insert holder blade. Clearly it needs to be two pieces with a bolt on base so shims can be inserted to get the right centre height, a once only job with inserts and if you accept flat top grind on HSS blades. This is probably the most rigid possible set-up, especially as it allows the deepest blade to be used. Similar arrangements are accepted on rear tool posts so why not at the front?
|Thread: Spiralux Drill Grinding Attachment|
These things are a nightmare! Especially when you get clones of clones and mixed up angles. Bottom line is that the ones with a tilted pivot post (General, Spiralux & clones) need the drill edge vertical and the ones with the pivot post vertical (Picador and clones) need the edge at an angle, sort of 5 to 5 ish, to work. The projection depends on the offset distance between Vee carrier and rotation axis. The shape of the little sheet metal stop also gets involved.
There are also subtle differences between those intended to sweep across the side of the wheel and those which run from the front. I notice the General instructions linked to show use of the front of the wheel whilst Picador and Spiralux instructions refer to using the side. I'd have thought that wheel diameter and drill point height relative to wheel centre would have been important is using the front. The Picador device is certainly much more civilised when using a narrow cup wheel, mine is 10 mm face, than when using the side of a normal wheel as advised in the instructions.
I believe it is possible to work out and demonstrate graphically what is going on so that things can be set "perfectly" from measurement for any size of drill. That said I've not been able to figure out anything that could be considered understandable by the general reader. (I'm none too sure I understand what I've figured out myself!) Hand waving, "its sort of like this" and step by step "works for me" instructions aren't too hard to get to but pinning things down properly is like nailing jelly to the wall. I can't help feeling that even the original designers didn't really have a complete handle on the geometry and settled for producing something which can be made to work by a determined user. A trained, albeit non practising, toolmaker friend says its a darn sight easier to learn to sharpen by hand than to learn these "easy" jigs. He may have a point! The original PlasPlugs design in the 4 in 1 sharpener set is actually pretty easy and works well. Dunno about the current version.
|Thread: Harold Hall QTCP, MEW 50, any one using it?|
As requested a picture of the two "bent" styes of Armstrong type holder posed next to a round bar at more or less operating angle. Various sizes and similar but different styles depending on maker. These are for 1/4 square tool bits, shanks on these are nominal 1" high and typically the sharp end will be about 5/8 to 3/4 above the support surface. Usually the bit axis will be 90° to the work with any special shaping ground on the tip. A 3" stick of HSS will usually do for 2 double ended bits.
Hope this helps.
Given the inevitable budget constraints, both fiscal and temporal, concerning Home Shop and Hobby activities I think there is much to be said for a system based on interchanging tool bits in nominally fixed Armstrong type holders. Provided of course that your lathe is large enough to accept Armstrong holders which may rule out anything below about 3" centre height unless the top slide is removed. Because the Armstrong holder mounts the tool bit with an upwards slope setting the bit to centre height also sets its projection to close limits. The optical centre height gauge described by Ted Wale in the November 2004 issue of Model Engineers Workshop is by far the best type, especially in this sort of application. I was familiar with the principle for many years previous to Teds description but never felt it would be enough better than what I was using to make one. Needing a new gauge to suit my Smart & Brown 1024 I finally got round to it and seriously regretted a quarter of a century doing things the usual way. Square tool steel is inexpensive compared to inserts and butt welded, forged shank tooling so its economically feasible to have a good range of bits ground to appropriate angles making it pretty much unnecessary to adjust the tool holder position in normal work. Grinding square tool bits to accurately repeatable shape needs only simple angle setting jigging. Some of the but welded tools can be a right pain with limited facilities.
Clearly a simple two slot block will suffice to carry the normal turning, bent to the right, holder and the face turning, bent to the left, holder. Simple stops to set the 180° rotation needed for interchange should be no great problem. Such blocks can be bolted up from stock sections. Similar holders will clearly suffice for parting tools and any insert tooling you may choose to use. If you use the common "mutant golf club" boring and internal threading tool forms hated by Geo.H.Thomas shimming must be resorted to. His eccentric holder and boring bar system would work well given a suitable block. Given a Tee slotted top slide switching blocks becomes trivial if complete assemblies with locking handles and Tee nut are made. In my South-Bend driving days I had multiple four ways made up in this manner carrying but welded tools which worked well save for the usual shimming tedium. The normal nut on a stud system shouldn't be impossibly tedious but, if so, there are various ways of arranging quick release. For example the centre stud could be arranged to be freely rotating with a cross hole drilled close to the top for a locking handle in the form of along pin. If an externally threaded sleeve with a castellated top is screwed into the tool block the locking handle can be passed between the castellations and though the hole in the stud. It should be no great problem to arrange matters so that third of a turn or so goes from locked to loose enough for the handle to be withdrawn and the block lifted away.
Obviously considerable refinements of the basic idea covering, for example, indexing et al are possible to suit individual needs. Clearly it works just as well with insert holders if pre-loaded blocks are interchanged.
|Thread: Ash Vac as Shop Vac?|
Thanks guys. looks like the Wickes version would be a better bet, double motor power should mean more suction and I like the idea of washable wet/dry filters.
Hafta look next time I go into a Tunbridge Wells.
Like Peter I've seen a Henry which had been used without a bag. Not pretty.
Like many others my shop vacuum cleaner is the uquibitous Henry. Although he is good at the suction bit the bag capacity can be limiting at times and makes swarf separation pretty much impossible so he isn't really the thing for primary machine cleaning. Sweep and separate the swarf being the order of the day followed by Henry to pick up all the little bits.
Next Monday our local Lidl is offering so called Ash Vacuums which appear to be a simple steel bucket having a vacuum motor clipped on top with appropriate filtration to let the air through and keep the picked up stuff in. The bin capacity is said to be 18 litres, much more than a Henry bag and, at first sight, it should be easy to clean things down with it then empty the collected swarf into the right bag for disposal. At £30 a pop it won't break the bank but $64,000 question is will it work OK as a shop vac.
Does anyone have any relevant experience, I get the impression that similar beasts can be found from normal retail suppliers.
|Thread: Which (round column) drill/mill?|
Realistically 32 mm is rota-broach or, if desperate, hole-saw territory. Comparing casual experience with the performance of my 15AY Pollard which will go over 30 mm I'd say 5/8 to 3/4 is about as far as a round column mill drill will routinely go with a twist drill. Maybe baby a bit bigger but it will depend. That said 1" and over is getting into better to power-feed area whatever you have.
As to build quality its the usual careful inspection of the one you are buying thing. Best is good used where the other guy has sorted all the silly stuff. If you are considering new purchase costs are well into the area where a good quality non Far East industrial machine could be found and fitted with an X-Y table. Or even do the Bridgeport J head conversion thing on the mill.
I have a square column belt drive, inverter motor, version (Chester Lux style) fitted with 3 axis glass scale readout which makes an excellent co-ordinate drilling machine whatever its limitations as a mill. Pretty much matches the Bridgeport as a drill but the Pollard is still ahead.
As always nothing beats a chance to play with a real machine, if you are in striking distance of East Sussex you are welcome to come and twiddle the wheels.
There is considerable over-emphasis in Model Engineer and Home Shop Machinist circles over the concept of levelling = setting dead nuts level. As Bogstandard says the object is firstly to mount the thing sufficiently rigidly to ensure that there are no cutting force generated inaccuracies and then to ensure that bolting down doesn't twist the bed inducing geometrical errors. Level is just an easy way of seeing if you are pulling things out of shape when bolting down.
First thing to note is that a precision level is one of the most monumentally frustrating things to use ever invented. Far better to get an adjustable clinometer with a sensitive bubble. Mine is Ministry Issue dated 1944 Ref no 18/4235, base is about 7" x 1", vial 30 seconds per 1/8" division and adjustment range 10° with degree an minute scales. In some ways a 20 second vial would be better but this does me just fine. Use done for years in wage slave days to set-up seriously precise optical experiments. If anyone knows a reliable one off source of appropriately sensitive vials it would be a nice MEW project.
Secondly you need a good flat bench-top to set your lathe on. Preferably a "dead" material which doesn't ring or vibrate. Given the purpose its made for decent quality kitchen worktop is indecently flat unless badly stored. Pretty oil and damp proof too, lasts for 20 years in ye olde gaden shed shop to my certain knowledge. Use a chunk of that for your bench top, take pains to get it nicely supported and sit the lathe on it with adequately large pads under the feet. It will sit mostly, or only, on three feet. With thinking cap on tight, its not that hard to get it sitting near as dammit equally on all feet by careful playing with shims and feeler gauges. Careful tightening down, with exploratory probing with feelers should hold the alignment. Unless the lathe is in a very sad way you should be in the region of a couple of thou taper over the bed length. Nice to trim it better but perfectly acceptable most of the time. Long work will be tail stock supported anyway.
If you have a white target and a decent throw a cheap laser pointer makes a good error indicator. Clamp it to the tail stock with enough offset to clear the head or on centre and fire straight thu the hole. You will see any serious move as you tighten down.
|Thread: adjusting gib on machine vice|
Its far easier to feel what's going on when adjusting gibs if you can remove or disengage the screw letting you test by sliding back and forth by hand. Gives a much better feel for WTHIGO, especially if there is a sticky bit.
Especially with an unknown history component I'd advise doing the strip, clean, careful inspection and make sure it all fits right without binding thing before trying to adjust gibs. In particular remember that the old, gone off oil, dust, stuff, swarf and gremlin poo mixture which builds up everywhere that isn't positively swept out can take a deal of removing. Keep your thinking cap jammed on tight and visualise where the nasty stuff gets swept to during the operation of the slides. On small lathes I've often found that alleged "lots of play 'cos its worn out" is actually due to only part of the travel being covered by back'n forth movement allowing thous of "stuff" to build up in the rarely traversed areas. Darned hard too. Vices suffer in the same way although its harder to feel. Usual symptom is holds nicely over part of the travel but pants where you normally use it. I like to undercut the dovetail sharp corners a fraction with a couple or three strokes of a saw blade or three square file and remove the sharp edges from gibs.
Check the gib to see if its straight and flat and inspect the pressure point dimples where the screws act for smoothness and clean shape. Similarly inspect the ends of the screws. Bent and battered screw ends working in manky dimples destroy any chances of good adjustment. If you find such damage it is perfectly acceptable to comprehensively curse the perpetuators. Seems to be a Gib Screw Over-tightening Fellowship out there. Also inspect the alignment of the gib where it rides on the adjustment screws. Its not uncommon to find one or more screws a touch out of line or a slight skew on the gib so it drags on the top of slot.
Don't be afraid to re-make a damaged gib, not difficult as the material isn't critical. Flat with a decently hard surface are the main criteria steel, brass, bronze are all fine, but it does need to be as thick as possible. Ideally all but filling the gap so it is stiff to slide in. Best way is to get ball ended adjusting screws and use the common slocombe centre drill operating through the screw holes to make precisely aligned conical recesses for them to work in. Carefully shape the top edges of the nascent gib and push it tight up into the top of the slot when drilling. Good idea, if you feel up to it, to add a dowel to stop any tendency of the gib to float back and forth on the screws. The dowel works fine with the usual pointed gib screws but their condition and alignment must be beyond reproach. A carefully re-made, fitted and doweled gib with ball ended screws can run at rather tighter clearances than the usual variety.
Edited By Clive Foster on 18/11/2010 23:46:15
|Thread: How to determine the pressure angle of gears|
Fortunately for those lacking high CAD skills, or even CAD at all, there is an adequate direct measurement method for determining the PA of normal involute gears. I lifted this from a reliable source and its worked out fine for me
Firstly you need to know the diametrical pitch, DP, of the gear, basically number of teeth per inch of pitch circle diameter. For practical purposes pitch circle diameter runs round half way up the tooth. As its always a whole number and only a few numbers are used best guess estimation is usually good enough unless you are watch making.
Given the DP take a measurement over any reasonable small number of teeth with whatever equipment you have. 3 to 5 teeth for a chord length of around 1/8 of a circle usually does just fine. Multiply the cosine of the 'PA' by 3.1416 and divide by the 'DP' add this to your measurement, this should be the measurement over one more tooth if its not the same, change the the 'PA' and try again.
10dp 14.5 pa, 30 teeth,
Measurement over 3 teeth .776",
Cos 14.5° = 0.986147
(0.986147 x 3.1416) = 3.04
3.04/10 = 0.304
0.304" + 0.776" = 1.080" which will be the measurement over 4 teeth if the gear is
Obviously 10 DP is easy on the maths.
In practice you only have 14.5° and 20° pressure angles to choose from for general purpose gears so the difference is usually pretty conclusive. Its not an exact to umptyfour decimal places calculation, just a nearest to result for separating sheep and goats. I'd be very careful with gears having heavily modified addendum, dedendum and teeth shape tho'. It works, after a fashion, with stub teeth but some judgement is needed.
There is probably a direct version for module gears but substituting nearest DP is good enuf.
Heavily engineered devices such as car and motorcycle gearboxes often include gear pairs which are way outside standard formulae. Especially Japanese motorcycle gearboxes where its not uncommon to find teeth numbers up to one tooth different from what the standard formulas give for gears of that DP or Module and diameter.
Edited By Clive Foster on 18/11/2010 23:09:49
|Thread: Edgar Westbury powered hacksaw castings.|
For stock chomping give me a decent power hacksaw any day over a small, import, bandsaw. A Manchester Rapidor does the donkey work for me but I do have a fair bit of space. Was always impressed by the little Kennedy in the lab at work. The crafty use of hexagonal material for blade carrier and guides gave impressive stability for a simple design. I'm surprised that none of the home build designs have stolen the idea, or the equally simple Rapidor square bar system, as the plain rectangular plate slide-bar is a right pain to get shake free and free moving as well as being very intolerant of small machining errors.
Worst thing about the small horizontal / vertical imports is getting a decent blade. Some right rubbish about and even some allegedly name brand blades can be very fragile. The small wheels seriously don't help, 10" or even 12" diameter would be so much better, but then the whole thing starts getting large. Had a right shock when trying a new commercial supplier for a 64 1/2 by 1/2 blade and being advised to get a 5 to 8 tpi varipitch at £38 + tax'n carriage as the one'n only blade. Hard to believe that something this sophisticated is made for the baby saw or that its appropriate. Using in vertical mode on thinner stuff might be "interesting". Does the team think I should try?
Picked up a three wheel saw "cheap" which had clearly had the improvised repair gang at it. Wheels were right size but plastic with treaded rubber tyres! An experimental buzz suggested they might actually work but the "improved" blade guides were hard on the nerves. Maybe the El'fins do have a point. Axminster do some nice roller bearing guide upgrade kits, two will be going on this when I figure out how. The annoying won't quite fit problem so no space for modified mounts.
My two most reliable knurling tools seem to be rather rare types.
One is a hand squeezed three wheel one rather like a front pivot nutcracker in concept. Two wheels in the bottom handle one in the top aligned so the work piece will be trapped between them. Handles are folded sheet steel, decently thick, and there is a post with several holes in it at the front so the handle spacing can be adjusted to accommodate different material sizes yet still permit squeezing with normal size hands. Goes up to approaching 3" diameter and is very effective. Theoretically a stop screw lets you set knurl depth but in practice its not effectively engineered. Anyway its a very hard squeeze to knurl over depth unless the material is really soft. Fine on alloy, brass, common steels etc. but I've never been brave enough to try stainless or potentially obdurate steels.
Seem to remember drawings for one just like mine appearing in ME mid 80's or thereabouts although mine was thrown in for free with a lathe bought from a dealer when I picked it off the floor "obviously no good". But we had one at work so I knew better.
The other is a Pratt & Whitney two wheel pivoting type, bought mostly 'cos I have a P&W lathe and no-one else bid on E-Bay so it came cheap. Its arranged so that the in use the pivot point is rather below centre height so the lower knurl is pulled up into the work. Conventional pivot head two wheel knurls are designed so the pivot is on centre height so the knurls contact the "work sort of together more or less". The P&W variant seems not to suffer double knurling troubles.
|Thread: Milling Machines|
My experience is that its not so much the rigidity of the machine that limits the cut taken but rather the volume of swarf so you should have no worries there. I have one of the handy dandy card sleeve and slider feed'n speed calculators which you used to be able to get pretty much for free from the cutter makers (mine is Osborn) and found the values given perfectly acceptable after the usual reductions in speed to get home shop friendly cutter life. With hand feed the actual tooth loads were more a promise than reality but I guess around 10 to 20 % under book would have been somewhere near. Avoiding ultra tiny, cutter blunting, cuts naturally. The machine came with a 3" brazed carbide face mill which it was perfectly able to handle on rational cuts leaving a decent finish so a 1/2" cutter is well within its capabilities. I got one of the Little Hogger sets from Chronos which made an excellent general purpose set running about twice as fast as book HSS speeds.
As I said previously my dislikes centred on work access and visibility not pure cutting performance. Before redundancy provided the wherewithal and necessity of building a 32 ft x 16 ft workshop I contemplated some pretty serious modifications to improve things whilst still fitting into the machine half of my 12 ft x 8 ft shed. Essentially I proposed to perform major surgery on the head castings to improve visibility, shift the dovetail column sideways, turn it through 90° and hang the modified head off a short Bridgeport style ram carried on the dovetail column. Clearly I'd not have contemplated that amount of work on a machine of unsatisfactory cutting performance.
I have what is basically an older, somewhat unique, version of the Chester Lux machine having a VFD controlled three phase motor with two speed belt drive but slightly shorter table. If you are in striking distance of Crowborough, East Sussex you are welcome to come and play, personal experience being far better than 2nd hand as what drives me nuts may not worry you at all. Heck its up for sale "some-when" so if you like it! Mine has an R8 taper and, for all practical purposes, will take as heavy a cut as I'm prepared to put on the Bridgeport which has officially replaced it.
The square head is very large which can make setting up work and observing progress annoyingly difficult. Especially on my shorter table it can be a right pain making room to swing the knocking stick when beating parts down onto parallels. The large head is also very heavy, with no positive drive on the tilt anything more than about 10 degrees offset is distinctly scary solo unless you have a winch or check strap to keep all under control. Powered elevation for the head is vary desirable, mine has a plain crank which is hard work. Possibly the very worst feature is that the spindle is well offset to the front of the machine and will not cover the whole table front to back so the official Y traverse is somewhat optimistic without "creative" work holding arrangements. I fitted a proper 3 axis glass scale DRO set to mine immediately after purchase which proved essential to make the machine immediately useable. After sorting a stack of niggly and head scratching problems the machine proved to be enviably accurate. I believe factory QC is better on current machines. Hopefully the depth stop arrangements have been revised. The gears need to be quiet as most of the time the head is about 6 inches off you ears, even with my belt drive the sound is noticeable.
If you have the floor space and the money I'm inclined to think the "2/3 rds scale Bridgeport" VTM-2 machines from Engineers Toolroom may well be best-of-breed in this size / price range. I'm darned if I can recall why I absolutely didn't like the round bar "ram" VMC / 636 type machines when researching prior to buying the Chester Lux style machine. Many users are happy with these so it was probably something personal.
|Thread: Drill Sharpening Jigs - Advice please.|
I'm sorry that John hasn't been able to report complete success.
Looks like I shall have to have a rummage for the analysis on drill points and swing jigs I started ages back to see if it can be made "ordinary guy friendly" with some numbers and plots to show what's going on. My recollection is that qualitatively its clear what happens but putting numbers in and comparing results to the real thing is less than easy. However in the intervening couple of decades some ideas for different approaches have surfaced so, once I get rid of this stinkin cold, we shall see if anything publishable can be produced. Given the number of swinging jig designs that exist and can be made to work by dint of sufficient effort the basic principle clearly isn't rocket science. But given that every design seems to cause problems for even the most instruction diligent users it looks as if the geometrical analysis has been less than exhaustive.
Despite the impressions given in certain quarters four facets aren't the be-all and end all either. Although very effective in machine guided situations they tend to be unstable in hand held use. Think of a masonry drill. These are basically 4 facet geometry but wander all over the shop given half a chance. Functionally 4 facets are spade drills. Even on an industrial scale 4 facets are easier so cone points wouldn't be standard without good reason.
|Thread: Sharp Swarf|
The magnet in a bag trick helps to grab small ferrous swarf which escapes the brush. Just turn the bag inside out to remove the swarf neatly trapped ready for disposal. If its a strong magnet you need a strong bag, cling film will do for small weakish ones.
Brass is the worst as it seems to have self injecting properties enabling it to crawl under your skin.
|Thread: Drill Sharpening Jigs - Advice please.|
I'm glad you think that will be helpful.
Of course its possible that your jig uses a combination of pivot angle and drill angle to get the required extra grind depth. If I recall things correctly the angle of drill edge rotation from the vertical used by the Picador type and the pivot angle of the General type are both about 15 degrees. I measured them a few years back but can't find the results, somewhere lost in computer space. I guess a combination of around 7.5° each should work and has some point positional advantages relative to the grinding wheel.
Worst point is that the grind is damnably sensitive to drill point projection. The further the point projects the greater the "cone" radius, the smaller the clearance angle and the less the geometrical increase in depth with swing angle. It takes very little extra projection to destroy the geometry. The standard design is barely able to cope with the small projection possible at the bottom end of the range. Ages back I looked into creating an offset pivot position to allow a bit more projection, say 50 thou or so but decided it was too much work for something I didn't really understand. Plan was to fit an offset end to the pivot pin, might have done it if the pin had been screwed in rather than cast in.
I suspect the American Delta and Atlas types with their horizontal pivot pins do operate with a little more drill projection. These more complex versions seem a bit more effectively engineered but apparently are too costly for the market.
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