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Member postings for Clive Foster

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: My new lathe and why is the combound .002 per line
19/02/2018 11:23:21

Agree that its easy enough to get used to a direct reading dial.

But given that everything else in the machine tool world works by depth of feed and that all the cutting parameters are, as they obviously have to be, specified by depth of feed it seems silly to have a different system for a trivial simplification. How hard is it to mentally multiply by 2?

If you have re-settable dials probably best answer to any confusion is to adjust things so you always finish with the dial at zero. Gets all the thinking out of the way first. None of this business of was it 0.375 or 0.357 to finish on. More professional as you get what you set too.

None of the "8@#€€ its 5 thou over" followed by scraping and scratching to get it down to size or, worse "8@#€€ its 5 thou under" followed by rapid trajectory into the scrap bin at about Mach1. If what you set isn't what you get then adjustment is easy until, after a rather short while you learn how to be right first time like the professionals.

Clive.

Thread: Depth of cut
19/02/2018 11:07:12

My handy dandy slide rule "window" calculator fro Osborn tools says 764 rpm(!) for a 1/2" cutter in tough or mild steel.

Says:-

End mills are for profiling so cut depths up to the diameter of the cutter, 1/2 " or 12 mm, and cut widths up to 1/4 the diameter.

Slot drills, aka centre cutting end mills these days, are for for slotting so cut width is diameter of cutter and depth up to 1/2 diameter.

Feeds given as 6 & 11/16" (!) or 170 mm per minute for a 4 flute end mill and 4 & 1/4" or 108 mm per minute for a two flute slot drill. Feeds top be halved for long series cutters.

Leaving aside the rather theoretical precision of some figures its important that you give the cutter something to bite on. The action of cutting tends to stabilise things, too shallow a cut promotes rubbing which is not good. Folk tend to feed too slowly. Also important to get rid of the chips. Recutting chips is seriously bad news.

Very shallow cuts merely reduce the life of the end mill. To a first approximation it can only make so many passes before its blunt so taking 1/4 of the depth of cut effectively means a quarter as many jobs before its done. You have paid for the sharp flutes all the way up the side so you might as well use as much of the length as possible.

Clive

Thread: My new lathe and why is the combound .002 per line
19/02/2018 01:53:03

Brett

Your dial is calibrated to give the amount cut off the diameter which is twice the infeed. Common on American market machines. Often called a "Direct Reading Dial".

Allegedly better for novice and casual users because you get the size change directly instead of needing to multiply the feed by two. Personally I think it downright confusing because the topside is still calibrated as feed so you have two systems. Easy to get muddled.

I guess your DRO system is set to read feed so the DRO changes by half as much as the dial to really get you mixed up. Most lathe DRO units have a multiply by 2 setting which will bring its cross slide reading into line with the dial.

Clive.

Thread: Couple of things at Lidl
18/02/2018 18:24:36

Pete

6" disks would require a totally impractical amount of re-working. Effectively you'd need to cut it right back to the motor assembly and start over. Including making your own tool rest / work table. Might as well start with a bare motor and be done with it.

The carrier disk fitted is quite thin, a touch under 5 mm, with a similar space behind it so there is limited room between the edge of the tool rest / work table and body for a proper grinding wheel or diamond lap disk. Boss appears to be around 35 mm diameter as eyeballed from underneath with the table removed.

I'm going to try it out as is with the paper disks supplied and, if that seems OK, get some finer ones.

Its only rated for 15 minutes use at a time before you have to stop and let it cool down. Its never going to be up to proper TipLap or similar tool standard but should do just fine as the second stage in a three step sharpening process viz :-

1) basic shaped of the periphery of the bench grinder.

2) clean up hollow ground surface left by bench grinder to have small lands "top & bottom" at desired angles.

3) hand finish to bright, sharp, edge with diamond lap or stone.

Clive.

Thread: What thread is this?
18/02/2018 12:00:26

Reckon pgk pgk has nailed it.

Another link for my Engineering Data bookmarks folder! Goes to show that you need more than one source as my usual go to doesn't show all the ones in that link. Most but not all.

Clive

Edited By Clive Foster on 18/02/2018 12:00:45

Poxy spell check, twice.

Edited By Clive Foster on 18/02/2018 12:01:28

18/02/2018 10:48:29

Peter

As its an automotive application and made to screw into plastic its almost certainly a special.

Flat top suggests its either ACME or Metric Trapezoidal form, see **LINK** , for brief details.

Unfortunately its too small for the standard ranges given. I'd guess either 9 mm nominal full diameter with 1.5 mm pitch in metric trapezoidal or stub metric trapezoidal. Too small to be a stub ACME version of the 1/2" x 16 TPI thread used for R134a gas canisters.

Found this useful link for thread calculations **LINK**.

Home page has links to lots more calculators **LINK**.

Thread: Levelling a lathe..yes that old chestnut again
15/02/2018 23:05:41

Chris

If you are using the tailstock centre odds are its a combination of chuck runout and the tailstock being offset a touch.

Nine inches is far too long a cut for a simple 36 mm (call it 1.5 inches) diameter bar held in the chuck. Normal rule of thumb is no more than 3 x diameter from start of cut to chuck jaws. Translates to 4 1/2 inches of cut. Half of what you are doing. Quick reference for that sort of thing **LINK** .

For a quick'n dirty check I put nylon or, better, delrin collars on the bar. Cutting forces are much much lower so you can get away with far more stick out. Should be OK with your 9 inches. Better to use thick wall tube rather than solid bar as lower weight means less tendency to sag.

If the collars are pretty much same diameter you need to verify that the tailstock is in reasonable alignment. Quick way is to fit the headstock and tailstock centres and slide the tailstock up the bed until the points pretty much touch. Ideally they should be exactly point to point. If not trap an old 6" steel rule or similarly thin bar between the points and adjust the tailstock so that the bar lies straight across the bed. If the centres are good and sharp this is a very sensitive test.

Really you should be making your alignment tests by working between centres. You need to get an accurate centre in each end of your test bar so its size is limited by the spindle bore. Hold it in the chuck with minimal protrusion, face the ends and put the centre hole in. Then set up with delrin collars at each end and make your test cuts adjusting the tailstock as required to get them the same. Ideally no adjustment will be needed if you et the centres point to point first but in practice small, affordable machines are rarely dead nuts. If need be you can work your way back along the bed to verify consistent behaviour using bars of different lengths. Three should be fine.

Personally I'm very skeptical of all this levelling and twisting the bed to make things accurate bit. Careful shimming of the feet so it sits evenly and a good clinometer on the bed during the bolting down process to verify that no stresses are being applied always worked fine for me when I had smaller machines.

Clive.

PS You got your picture up whilst I was writing.  Thats a pretty hefty machine.  No way are you going to twist that into line.

 

Edited By Clive Foster on 15/02/2018 23:13:04

Thread: Anyone brave enough ??
15/02/2018 14:02:04

Brian G

I'm impressed that the technique could be considered for aluminium. I'd have expected the high thermal conductivity of aluminium to soften the material around the hole enough for things to distort before a clean extrusion for the tapped hole formed.

Clive.

15/02/2018 10:48:31

Saw that technique demonstrated at a FAST (fastener industry) exhibition maybe a quarter of a century ago. Two pillar drills on the table, one for the hole one with a Pollard(?) tapping attachment for the tap. Just like the video. Looked really easy but a bit spendy. Worst point is the rather ragged end to the hole. Might have been a spring loaded blade tool to clean it up.

Man did say you needed good solid drills with plenty of power. I want to think he had a pair of the then top end Meddings bench type but it was a long time ago. Not Far East Imports thats for sure.

Clive.

Thread: 6x4 Bandsaw Problem
13/02/2018 21:52:25

Allegedly a short (1/2" long?) nick cut through the outer skin where the blade starts cutting helps circumvent the hard skin issue. Presumably because the blade is able to cut immediately and pulls the hard skin away in thin layers with the chips. If the blade merely comes down on the skin it skates around until the skin is worn through. Which is very hard on the blade.

Breaking in a new blade considerably extends its effective life. Unfortunately following proper break in procedure is pretty much impossible with those saws.

Feed rate and pressure is also an inherent problem with those small hobby saws. The usual spring thing is somewhat non-linear and generally doesn't allow enough feed.

Bottom line is you are asking a boy to do a mans work.

If you have space seriously consider an older, relatively inexpensive, power hacksaw for that sort of stock cutting. My £100 Rapidor is very effective and would soon have paid for itself in reduced blade replacement costs if I did the amount of heavy cutting you seem to be doing.

Clive.

Thread: Couple of things at Lidl
13/02/2018 11:13:21

Mark

I think the male threads are probably supposed to be 12 mm x 1 mm. Certainly the one male thread fitting I found lying about the place is very close to that albeit a touch undersize. Given that Lidl are a German company that would be logical. That particular one probably came off one of the pressure gauge units which I promptly tapped out to 1/4 BSP to match one of my stash of PCL fittings.

However I do recall making a male "Lidl" to 1/4 BSP female adapter for a friend. The thread in the air tool or accessory, dammed if I can remember what, went into a very thin wall casting so zilch chance of tapping out to BSP as requested. As I recall things the male thread was 11.5 mm or little less OD. Either intentionally undersize or poor QC. If it hadn't been nicely chromed I'd have said the undersize was plating allowance and it had missed the chrome bath. Not wishing to split the casting I had about 3 goes at it. 24 TPI A/F Dormer / SKF / Johanesson style chasers on generous 7/16 OD gave a nice fit. Firm and shake-free but no risk of splitting.

I guess I'm not the only guy who tends to remember far too many of the gory details about simple jobs that turn into total nightmares with no chance of recompense for the time'n trouble.

Clive

12/02/2018 12:07:20

Some decent looking air tools and connector sets coming up on Sunday down my way. Could use some of the connector sets but they are PCS style rather than the PCL type I, and most other folk in the UK, use. Total bummer. But £4 ish is still good value for two swivel connectors even after binning the PCS connectors in t'box.

If you do figure to change the connectors after buying the screw threads appear too be unusual. Not BSP as one would expect. The couple I did for a friend turned out to be Admiralty with 60° thread angle. Probably supposed to be something bit more rational but rather out of specification.

Clive.

Thread: Scaling up
10/02/2018 20:14:41

Time to be pragmatic about things. When it comes to models the outside, visible, part needs to be the right size and the inside part just needs to work.

So scale the outside. Compare the resulting bore / stroke / piston area with that of a similar model thats known to work at least reasonably well. If your scaled result is close enough for government work call if good and get on with the important stuff.

Clive

Edited By Clive Foster on 10/02/2018 20:17:51

Thread: Bench Grinder advice
08/02/2018 13:50:13

If your existing grinder is OK for rough grinding and you have a Lidl to too far away maybe consider the 5" / 125 mm Parkside disk sander currently on offer for finish grinding. Picked one up this morning for £ 30 and was favourably impressed. See post in the couple of things at Lidl thread.

Best way to exploit the sanding disc type is to use the periphery of your ordinary grinding wheel to hollow grind the main face then finish off at the desired angle on the disk. No need to get the whole face flat. For our sort of machinery a generous 1/16" or 2 mm deep flat below the cutting edge at the correct angle is probably ample.

If you put the nascent tool solidly on the rest and go straight in the hollow grind should be good enough for all the angles we need. Lifting the tool with a spacer increases the hollow. Theoretically you can compute the height of the tool relative to the wheel centre for any desired clearance angle immediately below the cutting edge but, in practice, life is probably too short.

Clive.

Thread: Couple of things at Lidl
08/02/2018 13:34:48

Picked up the 5" \ 125 mm disk sander this morning for £ 30. Parkside PTSG 140 B2.

Figured that it would make a nice basis for a Tiplap style tool grinder after up-gunning the tool rest and arranging a proper grinding wheel in place of the standard plain disk intended for self adhesive abrasives.

Checking it out was pleased to find that it runs up nice & smooth. Even more pleased to see that the standard tool rest is decently robust for an all plastic device. Probably only needs some positive stops on the tilt adjustment and some fixed angle guides for the table to ensure same grinding angle every time. Comes with two each of 80, 150 and 240 grit self adhesive disks. Quick noodle on t'net shows that grits down to 400 are readily available so maybe it will do fine as is.

A round-tu-it project right now but we shall see in due course.

Clive

Thread: 'Why Projects Fail ...'
05/02/2018 18:48:54

At the personal and Model Engineering end of things I reckon dear old One Track writing in Motorcycle Sport mumble-mumble years ago had it about right :-

"Do something [to your project] every day."

I inserted the bit in brackets so it made sense as a stand-alone sentence. Original was 3 words and obvious from the context.

Working that way keeps you in the habit of getting on with things and if you are in the habit you can pretty much always find an hour without really noticing. How long does it take to read the paper? Start pushing it back to "I'll work on it Saturday, or Sunday" can soon shift to "-afternoon" then "-evening" or "-every other" maybe "-once a month". Which just doesn't get the hours put in. After all one hour every evening comes out at more or less a days work.

I know exactly whereof I speak having wasted a couple of years not getting on with things, for all the right excuses, when twenty-twenty hindsight says an hour a night would put me three projects to the good. Extra galling when you know there and then that what you are doing is just filling time and of less than no value, productive or otherwise.

Heck there's over half hour gone right here checking the forum and posting.

Clive.

Edited By Clive Foster on 05/02/2018 19:03:57

Thread: Joining cast iron
04/02/2018 22:06:17

My practice is to glue'n screw this sort of thing. Not had a failure yet which proves absolutely nothing.

For practical purposes the tensile strength of appropriate adhesives properly bonded to suitably prepared surfaces is 1/10 that of cast iron which is around 40,000 psi depending on type and lots of other things. For example JB Weld and Loctite adhesives are approach 4,000 psi. Automotive panel bonding adhesives such as 3M 08115 are said to be a little stronger in practice although book values are similar at just over 4,000 psi.

According to this site **LINK** that is similar to the tensile strength of an ordinary hardware store 4 mm bolt and not quite half that of a 6 mm one.

The great advantage of adhesives is the sheer area of joint which adds up to considerable strength without stress raisers. Aside from the difficulty of proper surface preparation for maximum bond strength the great disadvantage of adhesives is poor resistance to peeling forces. An adhesive joint is, by definition, a crack in the material. Once you start wedging a crack apart the force per unit area at the tip becomes very large indeed so the poor glue has no chance. Generally properly sized mechanical fastener has ample strength to survive the induced stress concentration, considerably aided by the crack stopping action of the hole, so screwing and gluing gives the best of both worlds. Needs lots less screws than a simple screwed together joint.

Clive.

Thread: BF20/G0704 DRO mounting
04/02/2018 18:40:58

When I fitted a DRO system to my Chester Lux style mill many years ago I reworked the stop system to make it shallower using an ordinary hex head bolt instead of the cap head provided. I left a space between the edge of the table for access to the adjustable stops and hex-head set screw for the which replaced the standard Bristol style handle on the lock. Changed the hand wheel for a folding type with a longer boss to win little more space. From memory the hand wheel only needed to be moved out about half an inch, maybe touch less, to find space for everything.

mill_3.jpg

Space for spanner can be seen in the picture. Only just enough vertical space for the glass scale above the slipways and hand wheel boss. These days I'd go magnetic every time on a small machine.

table.jpg.

Unlike Bandersnatch I used the X stops a lot on that machine. My normal practice was to mill with X axis whenever possible, setting the stops when verifying clearances and travel. This may have been because I frequently found table travel limiting. I now have a 49" table Bridgeport and almost never use the stops.

Clive.

Thread: replacement for Dewhurst switch
31/01/2018 22:36:52

Agree with JonBerk that those Chester switches do an effective job. Used 8 or so over the years, mostly for other folk. No complaints and no actual problems with the ones I used myself.

Except for the missing wiring diagram. Certainly a head scratcher as, if I recall things correctly, they aren't arranged quite how you'd expect from normal practice. If Jon can't find his diagram I may be able to find mine.

Effective and reliable though they are they were never my preferred way of doing things. About four things I didn't like about them and one thing I don't really approve of. So many years since I've last had anything to do with them that I can't remember what rubs me the wrong way. But working on weapons systems research (and testing) for most of my employed life has perhaps skewed my personal sense of rightness. In a practical world you hafta use what you can get / afford and settle for 'Well it works OK.".

Clive.

Thread: Correcting drill press runout
31/01/2018 19:53:18

Mark

Glad you are sorted but don't give up on the 'junk" welded up chuck and arbor just yet.

I'd set up a true running, turned in situ if need be, stub a bit longer than the chuck is deep and close to its maximum acceptance size in the lathe. Grab it with the chuck and have at the weld with a HSS tool ground to a shape similar to D or E carbide inserts. Basically a diamond. Blunter, larger tip angle, within reason is better. That way you can get at the weld area with minimal cutting of the chuck and arbor. Weld will almost certainly be softer. Be a bit generous with your cut depth so as to be sure that chuck and arbor will separate once removed from the lathe.

Although the weld suggests that either the female taper in the chuck or the male on the arbor is damaged in some serious way I think it more likely that previous operator was inexperience, stupid or both. Frankly if you just loose a 1/16 inch or so of mating taper length it matters not al all.

If they are actually damaged cleaning either or both up is a nice exercise in precision setting up and careful machining. I've done 5 or 6, maybe more, over the years with every success so how hard can it be? Bit of thought, patience and not getting rush-headed about things gets the job done.

If the male taper really is seriously affected just lay on a decent layer of weld with an ordinary stick welder and start over. She'll be fine. That sort of approach is almost essential if you need to fit a chuck to a Fobco 7/8 which are notorious for having a longer than usual taper in the spindle so common chuck - MT arbor pairs don't reach in far enough to fit. It is within specified gauge lengths but normal practice is to make things shorter! easy show off job.

Clive.

Edited By Clive Foster on 31/01/2018 19:54:04

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