Here is a list of all the postings Cabeng has made in our forums. Click on a thread name to jump to the thread.
|Thread: elliott 00 omnimill|
Manny: I got my Omnimill 20 years ago, and refurbished it 15 years ago, when it had to be taken to pieces to relocate it. Then last year (or maybe the year before...or the one before that !) I had the table, sub table and knee slides re-ground and the gibs re-surtfaced with something similar to Turcite. This work was done by Brian Caddy in Nuneaton (http://www.slidewayservices.co.uk) - recommended.
I replaced the vertical head bearings on my machine only a couple of months ago. Not difficult if you want to use 'ordinary' bearings, you can get away with fairly crude methods of pulling off the old ones and installing the new ones. But the Elliott specification for the nose bearings is that they should be 'matched for back-to-back installation' - unfortunately, when you include that phrase in your purchasing requirements, the bearing price goes up by a factor of 3! £150 for a matched pair, so you wouldn't want to install those using a hammer and drift!
That means rigging up a better system, and making a few collars, tubes and spacers to ensure that that the races are loaded correctly and evenly during installation on the spindle, and whilst installing the spindle into the quill. I had to make the necessary bits, so if you live in the north west of England, you would be welcome to borrow them.
The top bearing is a single deep groove ball race, about £25 for a good quality one.
|Thread: Tool post|
Sort of... I borrowed a Swiss Multifix from a friend (he was going on holiday and didn't need it for a couple of weeks!) to try it out on my Connoisseur, then subsequently bought a clone from Rotagrip. Size A.
If you intend to sit it atop a Myford top slide, I think you would be wasting your money, as you wouldn't gain many of the advantages it has over a Dickson. Also, you're supposed to fit dowel pins through the Multifix into whatever it sits on, to accurately position it and prevent it from twisting on its securing bolt - I think that might be inadvisable with a Myford top slide, it's weak enough as it is, without drilling more holes in it.
The A size is too big for the topslide, it's not possible get even an 8mm tool low enough to get it to centre height, you would have to order the Aa size, of which I have no experience.
However... if you have a DRO fitted and don't need the topslide for most work, then a size A Multifix can be mounted directly to the cross slide via an adaptor plate - I'd say go for it, it is better than the Dickson. And as it happens, I've designed an adaptor plate, the cast iron for which is currently on the milling machine being carved to shape! It should be finished next week.
Disadvantages of the Multifix over the Dickson: 1) the cost of the tool holders - they're something like twice the price, 2) for the size A the 1675 holders are 25mm longer, so you loose 12.5 mm of space between the front and rear tool posts, and 3) for 10mm tool overhang tools must be at least 50mm long as the holders only have 3 bolts spread over their 75mm width, preferably 85mm to get a tool clamped by all three bolts.
|Thread: Stress Fracture|
You might have answered this in your clip, but if so, I missed it!
What material is the plate made of?
You have a PM re your AXA toolpost.
|Thread: S7 Newall DRO v Taper Turning attachment|
Some time ago (see above) I posted re. a saddle clamp designed in 1992 by Don Ainley, and said that I would provide drawings when I’d finished manufacturing one for my lathe. Colin Rawson has reminded me that I’ve forgotten about this promise (thank you Colin!), so I’ve now put the drawing in an album, along with a copy of Don Ainsley’s original M.E. submission and a couple of photographs. Here’s the drawing:
A mixture of imperial & metric units - I normally work in metric, but the measurements of the mounting stud position were taken using imperial measuring equipment! Anyone intending to make one of these clamps should note the note about dimensions and surfaces shown in red, and the panel top left of the drawing showing relevant measurements taken from my S7 & Connoisseur machines – it would appear that all Myfords are not created equal, and these dimensions do affect the performance of the clamp. It has been tried on grey, green & blue machines and works on all of them, but clamping is noticeably better on the blue one, for which it was made. The effect of variations in the Myford dimensions can be seen here:
The gap between the clamp and the front of the shear is greater on the grey one, the top lip isn't perfectly flat on the bed, and the clamp plate is more horizontal – so as the note on the drawing says, you should adjust the red dimensions to suit your machine.
To find the position of the mounting stud relative to the front of the bed a 1” parallel was clamped to the bed, distances between the parallel and the stud were then determined using slip gauges for the vertical position and a feeler gauges for the horizontal distance:
Apart from the 'red' items, none of the other dimensions are critical, so I haven't shown them, those that are shown are for information, and do not need to be slavishly followed!
|Thread: MEX 2015??|
Diane & Neil - thanks for the information, better than I had feared. Good luck with your efforts, let's hope that it actually comes to pass.
I've just been informed that the Model Engineer Exhibition has been cancelled - apparently announced at the SMEE AGM. Can anyone provide further clarification please?
|Thread: Indexable lathe tools|
I get my Sumitomo & Iscar inserts from H. B. Tools:
I'm 100% with the comments from Andrew & Ian, but if these are to be your very first lathe tools, i.e. you're new to metal cutting, then I would add don't go for inserted tips, but learn with HSS first. Go straight to carbides and you run the risk of seriously damaging your bank account. Asking how I know this would be to ask a silly question!
I only ever buy tips in a SEALED box, with the manufacturer's name & tip reference on it, and preferably with the cutting data on the label. The cutting data tells you what material the tip is intended for, the range of depths of cut and feeds it is suitable for, and the cutting speeds. Without that information you are working blind when it comes to cutting metal. If the label or the seller can't provide that information, don't buy the insert(s).
Here are two I can thoroughly recommend for model engineering applications, I've used these for umpty-one years:
Turning: Sumitomo CCGT060202N-SC-T1200A
Boring: Sumitomo TPGT080202L-W-T1200A & for a larger boring bar TPGT110302L-W-T1200A
|Thread: Parting Off MEW225|
My apoligies Neil, I misinterpeted your comment.
I was trying to make the point that if a tool cut without diging in, there was no reason why it should do that at somee point during the cut. Martin pointed out that variation in feed would have some degree of 'automatic compensation' that would avoid dig in, which is correct. In theory, at least, so after your last posting I tried it out.
800, 1200 & 1500 rpm, 22mm bar, close to the jaws of a near-mint chuck, 2mm tip (the same one that I've been using since the beginning of this exercise), parting from the top slide. Hand feeding, varying the rate of feed in a sensible/realistic manner didn't have any effect. Then tried whipping the handle half way round as fast as I could to push it in 0.040". There was a limit to how fast I could do that, due to feedback on the handle. Didn't dig in, carried on cutting after the initial grunt.
Then set the gear box to 24 tpi (0.040"/rev) and fed into the bar at 800 rpm, equivalent to turning the handle once in 0.15 seconds - a bit extreme, I think. It managed two rotations whilst slowing down, then stalled. The earth moved on this one. Was it a dig in, or just the motor pushing round with it's stall torque to make the work climb on the tool? I don't know.
Conclusion is that variation in hand feed shouldn't cause a dig-in, unless one does something really stupid, like putting the gear box on the screw cutting range!
To the charge of not giving sufficient consideration to variation in cutting speed as diameter reduces, I can only plead guilty. But easily fixxed. As the cutting speed reduces, the force on the tip increases, but as Martin has pointed out, the radial and vertical components should remain in similar proprtions. Hence the direction of F should remain more or less unchanged, hence the tendency to resist dig-in would remain unchanged. My last line therefore remains unchanged.
Neil: if a model engineer can't feed with reasonable constancy, and can't feel what's happening in the cut so that he can vary the feed, then he should be locked in his shed and not allowed out until he's learnt how to do it. It's called developing the skill.
Mark C: If parting was as easy as getting the tool geometry correct and setting the speed/feed, everyone would be able to get it to work without any drama
Well, once things like sorting out the machine adjustments, chuck, etc., have been attended to then yes, you've got it in one, it is easy. This easy:
As he was using the DRO to cut blanks off to length, perhaps this fits your suggestion for CNC - Child Numerical Control! Or just a very skilled operator?
Back to Martin.. on a postcard? Now, now, don't be silly, I don't do postcards! But you raise an important point for those using HSS, yes, high rake, sharp tool, is asking for trouble. Combine that with setting above centre height so that rake increases as depth increases, and it gets worse. Then sharp corners between the cutting edge and the flank - on an inserted tip there's always a small radius at these points, which influences the radial outward force - increasing this radius increases the radial force. So with sharp corners on an HSS blade there won't be as much outward force to resist dig-in. Maybe it would be worth stoning a small radius here? But make sure either side is the same, or the different radii would tend to push the tip to one side and cause other problems.
Blowlamp & Muzzer - I've used Iscar GFN1.6 and GFN2 since I was introduced to them 20+ years ago. Positive 6 degree rake.
Having gratefully taken repossession of The Good Book Sandvik, done some revision, and had a think about how to put this one together …. these sketches of what happens at the cutting region are based on two in the Sandvik book:
I-6: The chip is sheared off the parent metal as the work passes the tool, and flows across the rake face. The angle of the shear plane depends on the material, rake angle, feed, depth of cut and speed. Between the deformed chip and the rake face is the flow zone, where the speed of the material varies from near zero at the rake face to chip speed – material in the flow zone is therefore subject to shear, so there’s some force being exerted by the chip as it moves along above the flow zone, which in turn gets passed onto the tool.
I-25: Indicates the distribution of compressive stress in the work piece, which combine to produce the F, the force on the tool. Obviously, the magnitude and direction of F again depend on material, rake angle, feed, depth of cut and speed.
Once those parameters are set (e.g. parting steel, 2mm wide tip, 0.002”/rev feed, 6 degree rake angle, 1000 rpm), the magnitude and direction of the force on the tool is fixed, and will not change during cutting. So if the tool starts off cutting ok, it will continue in that vein, and will not have any tendency to dig-in part way through the cut. Full stop!
The major influence on the force and its direction are the side and top rake angles on the tool, for parting we’re only interested in the top rake. Increasing the rake angle reduces the force significantly, Sandvik quote a reduction of 1% - 1.5% for every degree more positive. Increasing the top rake also reduces the radial component, and although I can’t find any figures of % reduction/degree, it is obvious that it could eventually disappear altogether – this would be the point at which a tool would develop a tendency to dig in. But that is not going to happen during parting/turning operations, because the tool’s rake angle is fixed.
The example of drill grabbing when breaking through or opening out a hole is a different situation, and does not provide a valid comparison with what would happen during parting. It is, however, an excellent example of the influence of rake angle!
The rake angle of a conventional twist drill varies from centre to lip, from zero or near-zero degrees at the web, to helix angle at the lip, so say from 0 to 30 degrees. Furthermore, the point of a drill does not shear away the metal in its path, as a turning or parting tool does, but forces it out of the way by plastic flow. Which is why, if you stop the drill at the right moment, you get a raised pip on the underside of the work.
So you continue to break through, when one of two things can happen:
1) The flutes of the drill engage with the bits of uncut but deformed metal around the periphery, and the helix drags the drill in, or:
2) The gradually increasing rake angle reduces the tangential and radial forces to a level at which the drill can dig in.
Or a combination of the above.
As far as opening up a pre-drilled hole is concerned, obviously 1) above does not apply at the start of the hole, so grabbing is then down to 2) on its own. Of course, it’s not just brass that does this, steel can do it as well, as anyone who has tried to open up a hole in steel with an electric hand drill can attest. But it certainly is more prevalent with brass.
As a further example of rake effects, we need only look at how to avoid drills grabbing in brass – stone a flat on the lip, so zero rake all the way across the drill radius, or use a slow helix drill, with typically 13 degrees helix angle, so that the rake doesn’t go ‘over the top’ at the lips.
As far as Chris’s adventure with an aluminium tip is concerned, again it’s down to inappropriate rake angles. An aluminium tip has a top rake of 20 – 25 degrees, so cutting force down by something between 20% and 37% and radial force very much reduced, perhaps gone altogether. Additionally, there will have been some side rake that further reduces the radial component, and possibly an additional effect of the entering angle, if it wasn’t 90 degrees.
So I hope the foregoing has now convinced you that:
1) The reasons for drills grabbing in brass are readily explained, and relate basically to the rake angle at the lip of standard helix drills.
2) Comparing what happens when drills grab in brass with parting operations is not valid.
3) A correctly formed (i.e. with sensible and realistic top rake) and set up parting tool does not have any tendency to ‘dig in’.
|Thread: Poly-vee problem - S7 mod|
I looked at Speelwerk's scenario today, unfortunately it doesn't fit the once per rev feature.With the pulley diamters and spacing I have, any maximum (or minimum, or anything else) would only repeat once every 2.23 belt revolutions. Also the run-outs on the pulleys are well within the limits specified by Conti-Tech in their design manual.
Ian P & KWIL: the circumferential strand is indeed spiral, so I tried two different 6-rib belts two ways round each - no difference. Also did the same for the cut-down 4-rib belt, again no difference. Cutting it down to 4-ribs ensured that it wasn't contacting the sides of the pulleys, so any protruding matter was running in fresh air.
Andrew M & John F: I tried both suggestions in one hit - made a PTFE washer 0.020" thick, bored slightly undersize on the i.d., so it set itself up as a 'PTFE-Belville' washer when installed. It has stopped the shuffling, which only needed a very small force to restrict it - the pressure exerted by a DTI probe would stop it, even the stylus of a Verdict indicator reduced the shuffling.
So thanks for those suggestions, it's cured and the machine is now very quiet. But I still don't know why the pulley wants to move about!
I've changed belts 6 times, and then stripped the spindle, made the washer, and re-assembled the spindle, all in one afternoon. If there were an international competition for belt changing, I'd be at Olympic standard, I can do a belt change in well under 30 minutes now!
|Thread: Parting Off MEW225|
I've drilled 12 x 11mm holes (6 in brass, 6 in free-cutting bronze) x 15mm deep this evening, with a Dormer A002 drill. No dig ins.
I only seem to get dig ins when either breaking through into fresh air, or opening up a hole with a bigger drill. Blind holes (as per today) don't cause difficulty. Is that the same for Andrew & Chris, and anyone else?
|Thread: Poly-vee problem - S7 mod|
Andrew: They were indeed difficult to find! As I recall, the problem was the 30 degree contact angle, which seemed to be out of fashion amongst the major manufacturers. 7007B (40 degrees) and 7007C (15 degrees) were more readily available, but I wanted to stick to the Myford original design, and didn't want to use bearings by some unknown manufacturer. I got the bearings from this company:
They're not far from me, and say they specialise in finding obsolete bearings! Well, they did find them:
but they were a) much higher precision than I wanted/needed, and b) bloody expensive - but I did get a very good discount, so not too bad! I too made a bearing puller to install them in the headstock.
I converted my S7 to poly-vee belt primary and secondary drives back in 2012, since when I've had a problem that is sort of resolved, but not entirely.
To cut the grooves in the countershaft and spindle pulleys the otherwise finished pulleys were mounted on mandrels, and the grooves cut with a professionally ground HSS form tool, to ensure correct form and concentricity. The grooves run true to better than 0.0015" radial and axial run-out.
When running on the 2105rpm speed setting (and only on the 2105 range) , the headstock develops a clattering noise, positively identified as being caused by the spindle pulley moving laterally on the spindle and bumping into the back gear.
If I assemble the headstock without the back gear in place (so that the pulley has no restriction to its lateral movement) and run just the pulley, it shuffles around by something like 0.020", perhaps a bit more.
The shuffling gets worse as belt tension is increased, only disappears when the tension is so low as to be all but useless.
Now for the strange bit - it does this once per BELT revolution, which seems to suggest that the pulleys are ok, and indeed they seem to be - see above.
I've tried 3 different belts - Pixar (came with the Hemingway kit), Optibelt and GoodYear. All do the same thing.
I tried biasing the pulley shuffle towards the tail end of the spindle (to stop it hitting the bull wheel) by shifting the countershaft pulley leftwards, to try to hold the spindle pulley against the angular contact bearing assembly. But to stop the rattling the pulley has to be so far offset as to cause the belt to protest.
I discussed the shuffling problem with someone who is expert in poly-vee belts, he had not come across this before. He suggested it might be worth cutting a belt down to 4 ribs, as 6 ribs (as designed) was possibly over-belting the machine.
I did that, it might have made a small difference to the shuffling motion, but nothing significant. However, it did make a difference when trying to bias the movement - the countershaft pully only needed to be shifted left by less than half a groove width to stop the spindle pulley hitting the bullwheel, and the belt seems happy enough with that.
So that's how the machine's running now, no rattling and working ok. But I don't like things that I can't understand, and the solution is a bit of a bodge. I'd rather have it right, full stop!
So, can anyone shed some light onto this strange phenomena?
|Thread: Super 7 Headstock Set Up|
Alan & Ady1: Adjusting the spindle is a simple two-step job: 1) Set the pre-load on the angular contact bearings, which also pulls the outer races into contact with the spacing/oiler collar, and clamps the bearing ssembly against the step on the spindle, then 2) shift the bearings and the now attached spindle about to adjust clearance in the front taper bearing. The procedure described by Myford has been applied to countless lathes by countless model engineers over the centuries, and is well proven.
I can see the logic behind Ady1's procedure, but why depart from a method that is well-established and proven to work?
I don't know the answer Chris, but it's a wierd noise, as if the balls were bumping into each other. Once heard, never forgotten.
I've seen this reference to KWIL's taper bearing mod a number of times. What's the advantage, and what's involved?
|Thread: Gas Blowtorches|
Ian: from the smell of it, this one's paraffing powered, but I've never had the courage to fire it up!
Why Sievert claimed to have no record of it is beyond me. I never considered it to be rare, you have confirmed that. But I've never seen another one.
|Thread: Super 7 Headstock Set Up|
Forgot to mention:
1) The NSK bearings are still available, but I think the only ones they do now are higher spec. versions than originally fitted . My lathe has been wearing NSK7007A5TRDULP3 tail bearings for about 2 years.
2) Myford did introduce a revised front bearing adjustment procedure at some time, but as far as I know it never found its way into the manual:
Note the bit about the scribed line, which refers to re-adjustment of the original bearings. From my experience of fitting new bearings to my S7 and Connoisseur machines, it won't be far out with replacements.
Alan: All that 'loading' means is that the inner races have to be moved together so that the balls are in contact with the outer races, bearing properly on the outer tracks. Then to keep them there under varying conditions of load and temperature, they have to be clamped together a little bit tighter still - pre-load. But not too tight, or the bearings will suffer excessive wear and possible damage.
Do you have the manual for the lathe?
Whereabouts are you located?
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.