Here is a list of all the postings Iain Downs has made in our forums. Click on a thread name to jump to the thread.
|Thread: Lathe rigidity|
Well it's been 40 days in the wilderness, but I've finally made some progress.
In advance, I can tell you that the take-away is that you should NEVER take your lathe apart unless you have a working lathe!
The first thing to do was to make a piece to press out the bearing that I'd pressed in. No lathe you see, so I had to do some lathing on my tiny mill. I decided to do this with a rotary table.
Unpleasantly the clamps shifted (several times) during the work, so I ended up by milling the outside again.
How do you part off on the milling machine, I hear you say? Perhaps, a slitting saw?
Nope, my trusty new bandsaw! result is.
The piece fitted passably well
And have pressed the bearing on to the spindle, pressed the spindle into the headstock.
It was at this point that I realised that I needed a similar washer to press the rear bearing in, if I was not to risk damaging the damn thing. I reached for my lathe.... Oh, dear! It's in bits.
Back to the trusty milling machine. This time I decided that life was a little too short for rotary tables and slipping clamps. So out came my boring head. A challenge this time was that the bit of aluminium I had that was wide enough was deeper than the Z movement on the mill by a few mm. I in the end I bored to that depth and then remove the last bit with chain drilling and a file.
Drilling the innards, before boring out to 30 mm
. Again the clamps didn't hold well, so I went back to holding down with some normal clamps and switching to a clamp through the centre for the outside
My first attempt at this used a standard boring bar, but running backwards. This wasn't a good idea as the only real effect was to unscrew the boring bar head from the mandrel.
So I took a boring bar I made earlier and made a sort of trepanning tool (above). As the piece had moved before I'd finished the middle it was no longer aligned as you might be able to see from the photo.
Not a piece I'm awfully proud of, but it did the job!
And the bearing pressed home nicely!
The question on your lips, of course, is, 'has it made a difference?'
The answer is a definite *yes*. Firstly, there is no longer any lateral movement from the chuck under load. Secondly, it runs noticeably quieter. And thirdly, it seems to be producing significantly better surface finish in my limited tests so far!
With this all done now, I feel re-energised - back in from the wilderness and will get back to the steam engine...
As usual my thanks to all on this thread who've offered advice and support!
|Thread: What is this called?|
And just to complete the circle, here it is fitted in place.
The window still needs a little 'help' when opening, but it's much better than it was.
Thanks again to all who helped.
Many thanks for all your help.
Especial Gold Stars for Mike and Bill for (astoundingly) finding just the right piece and then finding it cheaper! (Yes, Yorkshire).
I know what it does - it's part of the catch system for a double glazed window. However, google is not being my friend here (or amazon or ebay) as I don't know what they are called.
And in place
I'm sure you all think I should get out my calipers, draw up a plan and make one out to mild steel, but I have neither the patience (nor probably the skill) to hack up something which probably costs a pound to buy! If only I know where!
Many thanks in anticipation.
|Thread: Lathe rigidity|
Well, I finally had a chance to get back to the spindle things today and have good news and bad news.
The good news is that the polishing has worked nicely. I can press the old bearing in with relatively little effort and there are no 'twangs' as it is pressed. Hoorah!
Next, following the advice in this forum I pressed the front bearing home. This was silly and I should have applied brains.
I can see that the 'correct way would be to press in the front bearing (like this), then pull in the spindle (with the force on the inner race.
However, once the front bearing is in place there is no way to assemble the gears on the spindle.
The only way you can actually assemble the whole thing is to press the front bearing on the spindle and the put on the keyway inner spacer and gears and press the spindle in place. this means that the pressure is on the inner race with the press going in on the outer race.
So now I need to unpress the front bearing. To do that I need to make a spacer (approx 56mm diameter so that I don't damage it on the way out. If only I had a working lathe!
I think I can make a suitable spacer on the mill and cut it off on the bandsaw. But I don't have the heart to start it today!
Old Mart - your advice is well taken, but you have to know what you are doing to know what tools to make!
Alan and co. - I get the same deflection on a 3 jaw chuck mounted directly on the spindle.
And I have bought a spindle mounted collett chuck - one from ARC as it happens. I didn't know they existed until an earlier post introduced the idea.
Before I get to check how well that works, though I have to improve the fit of the rear bearing, re-assemble the lathe and try again.
That's not going to be today though
Thanks for the clarification Neil.
The front bearing is likely to be a tight press fit (I'm not sure what that means, but that's my guess) requiring a lot of grunt on my press to push it in place. Thanks btw to the poster who said that you should only press on the part of the bearing which you were pushing in (e.g. the outer race and not the inner). It took me a while, but I can see ho to do that.
As you say, the rear one needs to move, but move with strong manual pressure or only move with a press?
Also, can anyone suggest the correct grit to use for the polishing? I'm on 10 micron at the moment.
Some time has been spent working on the spindle. John - I took your advice about a split lap.
I had a handy piece of 1 inch wide 3 inch aluminium bar which I cut some shoulders on, drilled, and bored out.
With this being the 'finished' product
The offset shoulders is not some clever attempt to apply differential pressure, but as a result of my 6mm tap breaking off in the left had hole. This was most annoying, partularly as it was my favourite spiral tap. Finished the other hole off with my traditional set and hten drilled and tapped to 4 mm on the left having reduced the shoulder as you can see.
Although the original advice was for valve grinding paste, I actually don't have any of that, but I do have a set of diamond grinding paste. I started off with what I think is 5micron (green) and after 10 or 15 mins I didn't see much change I upped to 10 micron (gray). I'm testing this by attempting to press the bearing home with my fingers after wiping the paste away.
As I was getting bored turning the lap by hand, I finished of my polishing machine.
Which seems to work rather well. Thankfully, there's enough throat to be able to take the spindle off without moving the lower plate so it stays nice centred.
I would like to ask if 10 micron grit is about right - and how long I should expect this to take. The last thing I want to do is to take to much off!
The other thing which I found was that the bore in the split lap was not round. it's a thou ish different across different axes. When you're boring on my little mill there is a good deal of vibration and I think that the head is more rigid in one direction than the other hence less movement and more cut.
I don't think this invalidates the lap, mind you, just something to think on in future.
Thanks for the comments.
It occurred to me in the early hours of the morning, that the front bearing doesn't really need to slide as long as the back bearing slides freely.
If the inner shell is jammed a little bit before the end of the shaft, then it is still firmly in place. It's the back bearking that certainly needs to slide to pull both bearings together.
Is this right/ If so I need only concentrate on the back part of the shaft.
Also, I don't think it's possible to support both inner and outer shells for all the operations. I think the order of operation is probably to press home the bearings in the headstock and then press the shaft through with the rear bearing fully supported. That leaves the inner shell of the front bearing pressed on the shaft.
Of course if the shaft is a slide fit then this puts less stress on the bearing.
The plan was to remove the spindle from the lathe and mount it in the mill with the unholy collection of components shown below.
Underneath the bit at the front with the cone is a spigot which fits nicely into the spindle throat. The top end of the spindle gets gripped by the 4 jaw in the mill spindle. the bottom end slots into the coney thing and the cone sits in a centre drilled hole in the marked up plate which is bolted to the mill. Once I drill the centre it's going to be difficult to do anything else with the mill until the work is finished so that's the last thing to do. As the spindle rotates some (probably) 1000 grit will take a little bit of the surface enabling a better fit.
So, next was to strip down the lathe and press the spindle out. The stripping down went fine.
I'd made a press out of scrapyard junk for the last time I had the spindle out. Whilst I just about got the job done there were some design issues. Mainly that the screw wobbled terribly which made the work piece move. The solution was to add a support column to the above the screw. A 2 inch steel bar with an exact inside diameter and slotted (and glued - green loctite, so nothing's moving it) into a recess bored in the top.
That's made a big difference.
Next to press out the spindle
The results of that were quite interesting. From earlier comments the outside of the bearing should be an interference fit and the inside a slide fit. As you can see below, even with the creaking from the press, the outer bearing fit proved weaker than the inner bearing - that is the bearing stayed on.
This wasn't ideal news. However, it did provide evidence for my theory that I wasn't able to correctly pre-load because the inner bearings was jammed.
How to get the bearing off? Press to the rescue.
I thought things were going OK until the bearing got to the rear bearing position. At which point the damn thing burst open! Bearings all over the shed...
I was able to get the bearing off, but I think I will need to to get a replacement bearing(s - might get the pair), I don't feel that it will ever be the same even if I do find all the balls!
Thank God for the Internet, eh?
OH - if anyone can provide more detail guidance about how to do this polishing and fitting, I'd appreciate it. I guess it's just a strip of wet and dry and keep trying the bearing. but I'm not sure what a slide fit consists of - and if I should lubricate to get it on.
I'm thinking I might try and make a spindle polisher with my micro mill.
I have a 4 jaw non-independant chuck on an MT2 spindle which will hold the back end of the spindle and I'm thinking of making a very short centre to slot into the other end of the spindle. That will engage in a centre drilled hole in a shallow bar on the mill bed.
I have the old spindle and with a bit of luck it might just fit.
he idea was to turn a spindle on the end of a short piece of bar which would exactly fit in the spindle, together with a threaded hole. Turn it round, put the spigot in the spindle, tighten in place with the bar and turn a center on it. The idea is to have no more than a bout 10mm from the spindle face to the point of the centre.
My first attempt at this has not been too grand. I cut a spigot in a piece of 50mm bar which very nicely fitted in the end of the old spindle. The new spindle unfortunately has a narrower aperture, so back on with the chuck and cut. Unfortunately too much, so the damned thing rattles and is easily offset with an over firm cut. So I think I will have to start again and be a bit more patient with the cutting and chuck swapping. Needless to say if I if I take the piece out of the chuck, the chuck off and replace the chuck and piece, the chance of it being centred is slim. I will consider my 4 jaw for this, though I can see a certain amount of frustration ahead of me.
In the meantime, it's time for a cuppa and some dinner. Not sure if I'll get back to it this afternoon - we're off out for tea a bit later - and there's only so far my patience will stretch in a given day!.
As an aside, stripping down and re-building the headstock the last time I did it (it's a long story, but I needed to change the spindle), was very time-consuming and frustrating. I'm trying to avoid that, but recognise that it may not be possible.
MY apologies. I have been mixing units which I should not. I want to work in metric, but my brain was wired in inches a long time ago.
For clarity. I am seeing around 0.04 mm deflection (40 microns, one to two thou). Working to micron level accuracy is well beyond any dreams of mine. thousandths of an inch may be within my grasp on a good day!
I see the same level of deflection on my 3 jaw chuck when mounted. so I don't think it's the collett chuck that's the issue.
I agree I should re-do the experiment with a similar bar mounted in a 3 jaw, and perhaps with a wider bar as well.
I wasn't aware of the spindle flange based collett chucks. Many thanks for the link!
I understand the idea of polishing the spindle. I guess I just mount the spindle on a lathe (probably between centres or something) and apply some very fine emery paper to it. I wouldn't expect to be able to do this with accuracy by hand. Herein lies my problem. Only one lathe!
It would be kind of fun to build some kind of jig to do this, but also time-consuming.
Any ideas on how to do the polishing without building another lathe would be most welcome...
Thanks, Jason. I looked into pre-load and good found the most useful information on my doorstep - here in the forum!
My particular concern about pre-load is that my spindle is an over-tight fit in the headstock. No only the outside of the bearings needs a lot of force to push home, but so does the inside (which should be a sliding fit). This makes the adjustment difficult and frankly I'm a bit scared to be too rough.
Lacking an appropriate thermometer I attempted to use mother natures thermometer and did as follows.
I tried to tighten the nut at the back of the spindle, ran the lather for a while (with chuck on) and felt the headstock. the first attempt probably moved the nut by 10 minutes (in Ketan's parlance) or about 30 degrees. I ran the lathe for about 10 mins, first at 500 and then at 2000 rpm. The headstock was barely warm. Next another 5 minutes and after that the headstock was definately warm to the touch (but not hot).
Here's the issue. The only way I could tighten the nut was with blows from a mallet (rubber in this case) on the spanner which seems to me to be not great.
I think turned my test piece (back to the bar in the ER32 collet) down to about 16mm (2mm reduction). in this case I was careful to do full passes from the end to the headstock, particularly with the final cut. I required 4 passes for the tool to stop removing material.
The good news is that the finish was better this time, though I can't be sure it wasn't me being better.
Quality at 18mm (before adjustment)
Quality at 16mm after adjustment
I was still seeing a lot of movement (1 - 2 thou) on the bar or on a chuck with moderate pressure - this didn't seem to have got better.
In frustration I decided to get some more scientific results so asked Mr Amazon to deliver one to me. £17 and reads up to 750 C!
So today I ran some temperature tests. I measured them at 5 points on the lather.
The black marks show a location on the spindle, 3 on the headstock and there's one on the rear of the spindly you can't see (E). I only measured these last two later on in the test.
Broadly, they all started off around 27 degrees (nice day, wasn't it!). I ran at 500 for five mins, 1500 for 10 mins and 2000 for 15 mins.
By the end I had
A - Spindle: 33
B - front of headstock 40
C - front top of headstock 39
D - rear top of headstock 44
E - rear spindle 41
From what I've read in the link I should be able to see 10 - 15 degrees more than this without unduly worrying about the temprature.
what concerns me is that the rear bearing seems to be hotter than the front one. This supports my concern that the inner race isn't moving freely on the spindle so isn't getting the pre-load.
I really don't know what to do next. I've made an extension to my spanner so I now have 2 feet of leverage not 4 inches, but this won't do any good if the front bearing isn't benefiting.
Any advice or experiences welcome.
IN another post, I complained of my new (cheap) ER32 collets not being accurate.
The usual good advice was received and I decided to do some measurements.
As practice I decided to use my micron indicator with a slide I've made to ensure alignment was spot on.
The original intent of the exercise was to see if I could use the outside of the collets to align the topslide to skim the collet chuck spindle. I've not quite got there, but some interesting results along the way.
This is the set up with a 20mm silver steel bar mounted in the collet chuck and then turned down to 18mm.
The first thing I checked was the straightness of the bar.
To do this, I set up my indicator and adjusted the height to get the centre of the bar.
This isn't a good photo actually as it shows a cylinder connecting the indicator to the slide. This reduced rigidity and I removed it for the actual measurements.
I measured the 'indent' (the depth the indicator was measuring) at 5mm intervals along the bar with the indicator and also took measurements of the diameter with a micron precision digital Micrometer.
Naturally, I took several sets of readings and found them to be surprisingly consistent (3 sets of indents, with a maximum spread of 8 microns, the micrometer was consistent within 2).
Here is a graph of the delta along the bar (the end of the bar at the start of the graph)
I think that the initial rise is because I took an extra cut on the first section of the bar, but for the rest it shows the bar being narrower near the chuck.
What's less clear is why the indent and the diameter are about the same. I would expect the diameter to have twice the variance of the indent. I have no explanation for this.
The bar was pretty round. Hard to tell how round because the roughness was significant, but to within a few microns (say 5).
Next I set up the collet and measure the indent between each slit at the inner and outer edge of the taper.
Incidentally, when I took a measurement, I would pull the lever out with the button on the indicator, move the piece and gently allow the lever to touch down. If I wasn't careful, I would move the cross slide which has about 0.1mm of backlash, rather ruining the accuracy!
In this case, pleasingly, the 16th reading was close to the first - within a few microns, so I reckon I wasn't jarring it too much.
This is a graph of my findings. B1 and B2 were the thick end and S1 the thin end.
Again relative movements in microns.
What this seems to show is that the collet is offset from the centre by something like 15 - 20 microns ( a bit under a thou), but that there is a skew on it - that is the peaks for the thin end don't coincide with the peaks at the thick end. I'd attempted to deburr the collet prior to the measurements.
What I did notice though is that even a small pressure on the bar caused quite a bit of deflection.
I put the indicator near the end of the bar and a luggage weigher next to it. Applying 1kg of force would generate a 20 micron deflection and 2kg around twice that. Beyond 2kg there wasn't much more movement.
This led me to wonder if I've not settled the spindle in correctly. I replaced it a while back with Tapered roller bearings and a great deal of trouble with pressing the bearings into place. They were VERY VERY stiff fits in the headstock.
My thinking is that the deflection could be a cause for the taper on the mandrel. if it was being pushed off by a thou at the far end by the force of the cutter, that would create a taper.
Can any one comment on this? Also, if this is likely to be the case, how can I improve it? I have tried to tighten up the nuts on the back end of the spindle, but they really are tight and I guess I'm afraid to provide too much force.
Finally, I had some good news.
I put in my MT3 test bar which gave pleasingly good results.
I measure the indent (with the micron indicator) at 0, 90, 180, 270, 360 degree angles at 25, 20, 15, 10 and 5 cm from the spindle face.
The maximum variation was about 55 microns (two thou) across the entire set of readings. Naturally this happened at the far end.
As a practical pointer, if you try this at home make sure to tap the test par home with a soft mallet. My original set of readings were depressingly bad because the test bar was loose.
So a slightly floppy spindle. What should I do?
|Thread: Collet Chucks out of true|
HI, Peak4 - that's an interesting idea.
I had something a little similar in mind to do today, until Madam suggested that we pop up to Saltburn for some fish and chips in the rain. Actually, quite a pleasant day out, but being an hour or so away it's used up my swarfing time.
Apart from looking at the nut (and photoing for proof), I had in mind to turn a mandril and put one of the collets on. I can check the collet for true on the mandrel (which will be true) and I can also use the collet on the mandril to line up the top slide exactly (within my skill level) with the collet taper.
I'm thinking I will start with some 20mm silver steel and turn that down to 19mm for the 19mm collett. I don't rightly know if I want to run through all the sizes to get a feel for the overall quality, but I might do two or three of them to check it out before I attempt to skim the inner taper. I might also try Bill's idea as well.
Not sure when I'll get round to it, actually. One evening would be ideal, but it depends on how work goes.
Jason, I'm not sure I'm quite following. I'm measuring the change in distance from the clock whilst I rotate the spindle. I agree that the actual measurement will be different due to the angle of the DTI, but I don't think it will change as the DTI moves into the check as the relative angle remains the same - the DTI is connected to the cross slide which I move in towards the spindle. I have also previously done this test with a lever type with similar results.
Thanks to all for the input.
I though (following Howard's advice among others) that I would approach this in a systematic way. Management summary: I'm still confused!
First I took an MT3 test bar and clocked the wobble.
I took most of my measurements 110 mm from the face of the spindle.
I'm going to use the term wobble to describe what I'm measuring. I'm not entirely sure I understand what run-out is - is it wobble (item at an angle to the spindle axis) or offset (item in line with axis bit not on centre). Accordingly, I will use an informal term so I don't get flamed
The wobble was of the order of 0.02mm. Hard to tell for sure as there was a definite tick which I think is a problem on the surface. However, under a thou seems reasonable..
This shows that the spindle is accurate and that there is no much in the spindle bore.
Next I measured the wobble in the chuck taper.
This came to around 0.06mm at three locations inside the bore. I measured again after re-seating and got a little bit less (around 0.05mm). I didn't try and see if the near points down the bar were in line (offset) or out of line (wobble). I've only just thought of it!
Having established that the chuck isn't crackingly good, I thought I'd measure some test bars in collets.
First up was an MT2 test bar held in a 16mm collet. Before trying this I attempted to deburr the collet. I took a small square diamond fine and run a a few passes on the insides and outsides of all the cuts. next I took a pick and pulled along the cuts to drag and swarf out. then finished off with a clean with WD14 and a rag. I should say that there was no evidence of buts by feel before hand.
And this was the test bar mounted in the collet.
I got wobble of 0.17mm at 75mm from the spindle face, 0.25 at 110mm and 0.36mm at 135mm. The wobble was entirely visible.
Next some 12mm silver steel. this was noticeably better -and better than the readings I'd taken before.
75mm - 0.06, 110 - 0.10 and 135- 0.14.
Next some 6mm scanner bar - like the bars in printers these should be ground and accurate.
at 110 mm I got 0.21mm wobble.
Finally, I took a piece of 20mm silver steel original intended for a crank, and did a few more things with it.
With the collet straight out of the box (first time of use), but cleaned:
0.30 mm at 110mm. Next I turned the rod in the collet (or possibly the collet in the chuck). This gave me 0.11mm wobble.at 110 mm.
I took the collet out and deburred as above and tried again. this time I got 0.24mm wobble at 110mm.
I tried again to rotate.(through 180 degrees) and got a wobble which was much less (0.07!).
As far as I can tell the low point of the wobble is the same with respect to the chuck / spindle regardless of the orientation of the collet or bar.
My best guess is that both the chuck and the collets are bad, so if the bad aligns, it's very bad, if it doesn't then not so much. This is not a nice thought and it doesn't seem realistic that all the collets are bad in a comparable way.
Any other ideas or diagnostics most welcome!
Yeah, Dave - I mentioned that in the post at the top of the page. Still well worth checking though.
I can see that I'll be known in 10 years as the 'badly fitted collet chap'
Just been to have my shoulder mauled by the chiropractor so, even though it's not my handle-turning shoulder, I reckon that tonight's not the night for machine tools
Thanks all, particularly Niels.
One of my concerns was having to wind the top slide ALL the way back to unbolt, make a very fine adjustment, wind it forward and repeat.
But if I can make the adjustment with the topslide in normal position that may work better.
When I measure run out on a test bar or an MT3 blank arbour, I get good results. When I do so with the sockets I get bad results.
However, I probably will try and measure again - though this is the 3rd time through the process!
I've measured the 'wobble' / run out on the ER32 tapers and they run to around 0.08mm.
I've also double checked the spindle and there's none (to the limit of my ability to measure.
So the chucks aren't brilliant.
I'm up for attempting to re-machine the ER32 taper in principle, but concerned it will end up scrap.
How I would approach this is as follows.
wind back the topslide, loosen the bolts holding it and set to exactly 8 degrees with my aldi angle gauge.(actually it will be 98 degrees as I will measure against the cross-slide edge).
put in the dodgy chuck and tighten up with the bolt.
take fine cuts at high speed (1500rpm?).
Try measuring again.
From what I can make out if the angle is within a few tenths should kind of work. Mr Hall mentions 'within a few degrees' but that seems implausible.
Do you think that would work OK?
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