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|
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?
I had cleaned the MT3 taper in the spindle and I had learned about snapping collets the last time Jason told me off (;)!
But always good to check...
Next time I'm in the shed, I'll check the taper of the chucks - probably at two places (depths in the taper) and also check the colletts for mess.
I suppose that I can check the wobble on several bars with different colletts and if they are all similar it's the chuck if they are wildly different it's the colletts.
I think I did and I think it was out. However, I will check that a bit later on.
A while back I bought an Mt3 ER2 collet chuck from eBay which I've not used much until recently.
Whilst turning some 12mm silver steel I noticed a wobble and checked it out.
I found the body of the chuck had a wobble of 0.06mm and that amounted to 0.6mm at around 200mm from the chuck face.
I looked around at alternatives from reputable UK manufacturers and found them to be around 3 times the price.
So I thought I'd have a punt and hope that mine was a Friday afternoon job and bought another one.
This one had a relatively small wobble, though it took the form of a depression around 45 degrees of rotation with the rest being pretty solid.
I measured both chucks again, this time with a 16mm test bar. Chuck number one showed a wobble of 0.36 mm 40mm from the chuck face (110mm from the spindle face) and number two was much better (!) at around 0.15 mm.
I put a test bar in the taper and measured wobble at the same place relative to the spindle face (110mm out). This showed more or less no deviation (under 0.01mm) except for a tick which probably a defect in the test bar (which I regret to say has managed to rust).
I also tried turning the chuck in the spindle and that established that the error was in the chuck not the spindle.
So I expect the advice from the assembled will amount to, 'if you buy cheap, you get sh*t', which seems correct. But what should I expect? ANd what do I need to pay to get a decent quality?
And is it likely that the collets are the problem rather than the chucks?
|Thread: Engineers blue alternatives|
I've spent some time using the sharpie approach, for marking, but not found it very useful for other than simple tasks. As soon as cutting fluid hits it, it's gone.
At the last show I invested in some dychem marking blue and it's been great. The only drawback is that it takes longer to dry than the sharpie.
|Thread: Steam Engine Number One|
Back to finish the job.
Having got the front side of the flywheel I set about carving out the back side. After some dithering and advice, I ended up by holding it on the inside of the flywheel shoulder with my 3 jaw.
This worked quite well though the piece was a bout 0.1 mm off-centre taking the outside of the rim as true. I had some thoughts on that - later.
Rather pleasingly, the trepanning on this side went really quite well. By now I'd ground the very hell out of the treppaning tool and obviously the million monkeys approach has finally worked. I think that a bit more relief on the sides of the tool helped.
Here we are a 5mm deep groove with a 3mm wide tool.
I took a few more cuts beside it - these being considerably easier than the groove itself - until the groove was side enough to get a 'normal' tool in.
Once this was done, I turned the flywheel round to dig out the rest of the front side. This time, gripping the centre of the front side in the chuck, but bolting it through the spindle to give it a bit more strength.
This was gouged out with a combination of a pointed tool (hss on the right) to dig out the bulk and then carbide left and right knife tools to come up cleanly to the rim and centre hub (well, cleanly for me!).
I'd decided, though that 0.1mm of centre wasn't good enough and made a stub mandrel to mount it on and tidy up the back side.
I'd learned some tricks for this from Harold Hall, who said that you should put the topslide to a few tenths of a degree to put the taper on. When I came to measure this up, I found it was already about 0.6 degrees out (in the right direction)! I must go back and set it up correctly now I've finished!
And here is the flywheel on the mandrel being tidied up.
I still need to cut a keyway, to do which I need to make a broach, but that can wait until nearer the end of the process.
Here's the flywheel on the Crank.
Next I'll be assembling the con rod, cross head and so on. I've all the parts just need to turn the rods to the correct length and connect..
|Thread: Stub Mandrel in Aluminium|
I did as suggested and just about the other side sorted out. The wheel was about 0.1 mm off centre held in the 3 jaw on the inside.
After taking off the bulk of the metal this way, I reverted to the aluminium stub mandrel to finish back to more accuracy and it worked a treat.
It's not pure aluminium - I had some of that a while back and it was HORRID to work.
It turns very very nicely. Much better finish that steel or cast with more or less any tool.
I hadn't thought of holding it by the inside of the rim. I'm not convinced that the chucks I've got extend that far.
However, it's worth giving it a go. Chatter is a problem with my machine pretty much all the time, so no need to make it worse!
I want to turn the back side of my flywheel (1 inch deep, 6 inch across) mounting it on a stub mandrel.
It has a 22mm bore.
I have no steel around that size, but I do have a piece of 25mm aluminium bar which could be pressed to service.
Is that a good idea? Or is it to soft?
Just to add a note, I then need to turn it round and finish off the first side so it needs to go on twice.
|Thread: Steam Engine Number One|
This last week or so has been about the flywheel.
As usual, I wouldn't have done it this way if I'd thought about it....
I'd bought a 1 inch thick piece of 6 inch diameter cast iron at the doncaster show for the flywheel, think that this was about as big a piece as my 7x14 would cope with.
Needless to say, this isn't going to fit in a chuck (not on my kit anyway). After pondering for a bit, I decided that the thing to do was to screw it to my faceplate, face one side and hollow it out leaving a hub. I'd then hold the hub in a chuck face the other side and add a hub, then turn round and finish off.
I marked the centre of the M6 threaded holes in the faceplate on the flywheel metal, drilled to 6mm (a bit more as I was a touch out) and counterbored to get some bolts in. The screwed it to the faceplate with some washers to stand off and mounted the faceplate on the lathe.
What I SHOULD have done (I think) is to glue it to a sacrificial plate of some kind and bolt that to the faceplate.
This way I had the issue of the interrupted cut on top of the hollowing (trepanning operation).
Anyway. I tidied up the edge with a indexed cutter.
One 'interesting' aspect of this sort of job is that the cross-slide has less movement than the radius of the work (even with a Wyatt modification), so you have to work on the outside and the inside of the toolpost. In this case I don't need a smooth face, so it's not actually an issue.
Then came the 'interesting' part. Digging into the face (trepanning) in order to get the middle out.
voracious readers of the forum will know that I had to seek advice on this from the beginners section. The resolution for me was to take the top rake of the trepanning tool, which reduced the chance of it digging in.
Nonetheless, this was a delicate and time-consuming operation. Having got a channel in which I widened with the tool, I could then get something more meaty in an carve out more of a hollow to leave me a hub to hang on to.
There! with some imagination you can see a flywheel starting to form.
And with the next step (boring the centre hole, first (image) with a carbide bar and then with a HSS tool for the final approach..
And I seem to have got this reasonably accurate. A silver steel offcut fits in rather nicely (same diameter as the crank)
However, i've changed my mind about holding it in a chuck. What I think I'm going to do is to make up a stub mandrel, face the what is currently the back part and then turn it round and finish off the hollowing out.
In fact, there's an argument for saying that I should have started off with the hole and done the rest on a mandrel. I'm not quite sure how I'd have made an accurate hole without the lathe. My mill isn't up to the job, I think.
|Thread: What Did You Do Today 2019|
Today, the plan was to build a shed for my shed.
As you all know, according to the Oxford English Dictionary, a shed is defined as, 'An enclosure in which your wife insists you keep the things she will not have in the house'.
That's all very well, but what happens when you don't want them either? In my case gardening equipment (we don't have a garden), paint and bits of wood, but most particularly recycling. No the council doesn't collect it. And I'm torn between pride that we recycle so much and shame that we have some much packaged stuff. I blame Amazon, personally.
Well, the obvious solution is to give your shed a shed so that the rubbish flows downhill.
This is my shed
It's quite full. Even after several attempts at re-organisation.
And this is the shed's shed.
This was going swimmingly until I came to spray the back, before pushing it back into place. I discovered two things about cheap fence sprayers. Firstly, they are not very accurate and the spray gets everywhere.
Secondly, if the delivery tube isn't as securely fastened as you thought and it comes off under pressure, it makes ONE HELL of a mess.
ALL over our wall. ALL over our neighbours wall! They were quite understanding as I scrubbed the mess off, but I'm relieved that their Mercedes sports car was not in its usual place when the accident occurred. There's only so much you can forgive!
Still got to finish off painting, but I feel there might be a brush with my name on it.
Yesterday a great disappointment arrived in my inbox. It was a VAT free code for Clarke Tools.
I imagine you re-reading that sentence, thinking me mad. In fact I'd been looking forward to this, having decided my birthday present would be a Clarke MIG welder, but a want and not an immediate need. So I'd decided to wait until a VAT free offer came along and so save 20% (which for one of the bigger domestic Clarke's, is quite a lot).
Still puzzled? Well, it happens that last week, I talk SWMBO into letting me buy a Femi bandsaw instead.
Having just spent £300 quid on one of these beasties (which seems very nice, thank-you), I would not dare to even hint at the potential savings the VAT free voucher would give.
So if any of you would like to buy a welder (or anything else Clarke) at 20% off, drop me an IM and the first past the post can have the voucher code.
And I will hope that the next VAT free voucher comes at a suitable time - long enough for Madam to have grown complacent and not too far in the future that I get too frustrated.
|Thread: Treppaning a flywheel|
As usual great advice.
The key was to take off the top rake. It's now 0 degrees - well, it might be one degree as per Andrew's suggestion, my hand grinding's not that precise. But it's no longer 10.
I reckon the rake was making the tool dig in and catch which was the heart of the problems.
Still requires a good deal of delicacy.
I could only get in about 1mm without it starting to jam, even though I'm convinced the relief was adaquate (and I kept tuning it), but in this case I didn't need a narrow slot so just plunged in next to it.
I also had a bit of a go at the point technique once the trough was done to start taking the bulk of the metal off.
As you can see it's starting to come together!
So, I will thin the tool and reduce the top rake and see how that goes.
Whilst my lathe runs in reverse, the cross slide doesn't go past the centre, though that would be a nice thought.
The holes were only drilled because I could think of no other way of holding the piece. Neither of my chucks come close.
Ah, damn. It's just occurred to me that i could have glued it to a base of some kind. That would have made much more sense.
Great advice as usual, but a bit too late to action tonight...
Thanks to all...
I wonder if I'm using the wrong terminology.
This is the thing I'm trying to make.
A model of it anyway. There's also a recess on the back side, but 5 mm deep not 15 (though this is a manufacturing requirement rather than a design requirement. I think).
This is where I am.
I'm digging into the face with the trepanning tool and then was going to go sideways probably with a right hand knife tool.
MOst of the progress you see there was actually with a knife tool with at an angle digging in a bit and then to the right, followed by a knife tool the other way to the left.
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