Run out on a rotary table

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Iain Downs on 28/03/2017 11:14:28:

So. Since I have a long day working from home, I took a brief break and got my mike and the pentagon out.

[…]

[a] Curiously this is not consistent with a thinner end in two orientations.

[b] None of this relates to the run out which would simply result in the pentagon being off centre with respect to the axis of the bar. That would take quite a bit more measuring which I'm not going to do in this case.

.

[letters added for convenient reference]

Interesting result, Iain … thanks for doing that so tidily

[a] that might indicate that the chuck jaws are angling the workpiece slightly off-axis

[b] I think I must question that assertion [if by 'run out' we mean simply that the taper is not concentric with the axis of rotation] … the geometry is more complex than you suggest, and the resulting pentagon would not have equal angles.

I look forward to seeing Dave's analysis.

MichaelG.

[JasonBModerator @jasonb]

If you don't have a tailstock then rather than cut from the side make the cut from above and use a machinists jack in its simplist form of two nuts and a length of studding will do, you probably have some in your hold down set. Just adjust the nuts until they support the work from below.

Could also clamp a block or angle plate agaist teh opposite side of the work to do the same thing if you still want to cut on the side.

If it were due to flex I would expect the first cut to deflect the most, then three with similar deflection and the last with the least error. Did you lock the table for each cut? levers look to be in the loose position in the photo.

Simple jacks

[not done it yetParticipant @notdoneityet]

As I see it, the run out was not checked on the workpiece.

"I checked the run out on the table with an 8 mm test bar (taken from a scanner in an MT2 collect. I got around .14 run out over 50mm. The actual milling was done nearer 100mm which would put it between .25 and .3 out."

Run out would have been better checked as the rotary table was adjusted throughout a complete turn, shirley, not just along the bar at one point, as the above suggests. Until that is determined there is only guessing as to how any discrepancy between target and actual measurements may have arisen. Or have I missed something?

[SillyOldDufferModerator @sillyoldduffer]

OK, so this is what I did. I haven't measured the end results like Iain yet or come to any conclusions.

First I set my HV6-type rotary table up:

As table is bolted down at the front it tends to twist slightly as the bolts are tightened. I use a set-square to check all is well because of the 'run-out' this causes.

To discourage tilting, the table is clamped at the back.

The test rod is a 250mm length of 10mm diameter Bright Mild Steel. The end has been faced and a centre drill used to make a pocket for the tailstock's fixed centre. About 210mm protrudes from the chuck.

At 220mm from the chuck turning the table revealed the run-out to be 0.2mm. Tightening the table's locking clamps improved this to about 0.1mm. On the other hand I was able to bend the rod 0.53mm with my finger.

Fitting the tailstock made a considerable improvement. Firstly the 'run-out' at the end of the rod is reduced to zero. Secondly the finger test requires a lot more force to move the DTI. This picture is blurred because I was pushing as hard as I could. This is about 0.04mm and I was able to reduce the deflection further by tightening the tailstock.

By calculation I found that a pentagon required the table to turn 72° per flat and that the depth of cut needed on a 10mm diameter rod was 0.95mm I actually used my DRO to cut 0.9. In terms of accuracy the DRO is +/- 0.02mm and it's quite easy (for me) to overshoot by up to 0.04mm when cranking the mill table. I used a 20mm diameter TiN coated 4-flute HSS cutter to make a sideways cut with the cutter positioned to use the upper part of the blades. The idea was that these will be less worn and more rigid.

Each time I turned the rotary table to cut a flat I clamped it and all the other non-moving axis. I used the set-up on the same rod twice, first with the tailstock and then without.

Next post: the results.

Dave

[SillyOldDufferModerator @sillyoldduffer]

My micrometer isn't in it's box. I wonder where I've left it.

Without a tailstock the rod visibly vibrates during cutting, perhaps as much as 2mm, and the tool chatters. Although not scary bad it doesn't sound as smooth or feel as controlled as the more rigid arrangement.

Anyway here's the pictures:

It's fairly obvious that the tailstock supported pentagon is better looking. It also appears to be more regular. I'll post the measurements as soon as I find that pesky micrometer.

Dave

[SillyOldDufferModerator @sillyoldduffer]

I've been busy taking measurements and drawing graphs. All dimensions in millimetres.

These tables are roughly equivalent to Iain's change over distance. This one shows dimensions when the work is unsupported:

And this is when the work is supported by a tailstock:

Graphically the difference looks like:

The tailstock supported cut is closer in shape and dimensions to theoretical perfection than the unsupported cut.

The change of cut depth when the work is unsupported is up to 5 times worse than when the work is supported. In both cases there is evidence of a taper.

Next I lathed the ends off the test piece so that I could measure the widths of the flats, ie the legth of one side of the pentagon.

The figures reveal much more variation in the unsupported ('free'  pentagon, than it's Tailstock supported equivalent.

This graph overlays the shape of the pentagon over about 8mm length of rod. (I wish I'd taken longer cuts!) You can see that although the table holds the 72° angles the dimensions of the pentagon change. There's a hint of twist too, though that might be a coincidence.

The equivalent graph when the work is supported by the tailstock is neater. The lines almost overlap showing that the pentagon is dimensionally stable and there is no hint of twisting. Only the blue far end edges out on axis 2, this being consistent with the slight taper noted earlier.

Conclusions.

Iain's Original Post expressed a concern about the run-out of his Rotary Table, which is a Warco HV6 like mine. He found 0.14mm on a rod 50mm out from his chuck.

My HV6 has a run-out measured at the centre hole of the table of less than 0.02mm. With 200mm of 10mm diameter rod protruding from a 6" chuck, I found run-out of 0.2mm at the end of the rod. Tightening the rotary table clamps reduced this to less than 0.1mm. I suggest this is comparable to the error in Iain's set-up.

I was able to bend my rod with my finger by 0.53mm; this is certainly less force than can be applied by the milling machine and it's lead-screws . When cutting the rod without benefit of a tailstock the end of the rod vibrated by about 2mm at the end and there was chatter.

The figures show that the dimensions of unsupported cuts were about 4 times less accurate compared with those done when the work was supported. The figures also show that the dimensional changes of unsupported cuts are inconsistent, presumably because the rod is acting as a spring, releasing energy whenever it can. The photographs confirm that supported cuts are better, not only in terms of dimensions but also the finish. This confirms the classic advice that care should be taken to ensure that work be held as rigidly as possible.

Though not as bad as I expected, I was unable to make a good pentagon without a tailstock. As my 'run-out' was similar to Iain's, I suggest my results show that his poor results are more to do with not sufficiently supporting the work than a defective table.

Is my table more accurate than Iain's? We don't know. My base run-out measurement was taken from the centre hole with the table flat, which is as good as it can be. Iain measured his run-out from the work, which will amplify any error, not only in the table, but also in the way it was configured.

In that respect it's worth considering all the possible sources of error; I used a set-square to align the table; I used a DTI to align the tailstock and confirm it was working; I clamped the table locks before taking a cut; I clamped the unused mill-axes before taking a cut; and I used the fattest milling cutter I own as close to the spindle as I could get. Even so I look forward to someone pointing out where I went wrong. (Not least me being cack-handed.)

I haven't tried cutting a pentagon to see what happens with the rod deliberately shimmed in the chuck to artificially create a significant run-out error. Perhaps Thursday…

Cheers,

Dave

Edit: pesky smilies!

Edited By SillyOldDuffer on 28/03/2017 16:43:12

[Iain DownsParticipant @iaindowns78295]

Wow! That's a bit too professional for me …

Well, I'm going to have to re-do my pentagon but trying it properly to start with. That is putting it in a collet not a chuck and not taking it out and really won't be before the weekend.

For information I was cutting in several chunks with a carbide 10mm tool at top speed (2000). The actual finish is actually very good unlike the one in Dave's earlier post.

Again, for information, I was measuring the run-out by rotating the table with the test bar in a collet and a dial test indicator resting on the top. not along the test bar.

What I've just done is to take the table of the mill and put it on my surface table to see if the table itself is flat. In the process I note that the MT2 taper appears to be integral to the table and not an insert as someone suggested.

I rotated the table and measure the relative height every 20 degrees or so (the slots made that impossible in all places). the indicator was around 53 mm out from the centre – by coincidence close to the distance I was testing run out on my test bar.

My results look like this.

In truth, I'm not quite sure what to make of this. I think it says more about the lack of flatness of the table than any run out. If the taper axis was perpendicular to the surface of the table, I would expect about the same gross error at the same distance along as across. I'm only seeing half of that and the shape of the error doesn't make much sense in the context of a single angle incorrectness.

What my original post was really asking (before experimental physicist, Dave, took us to the heights of professionalism) was if the table could be adjusted. I mainly asked this because the rear of the table appears to have a sort of push pull arrangement of grub screws and I wondered if they could be used to correct the tilt.

Iain

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 28/03/2017 16:41:37:

[…]

I haven't tried cutting a pentagon to see what happens with the rod deliberately shimmed in the chuck to artificially create a significant run-out error. Perhaps Thursday…

.

Great work, Dave !!

… Lot's to think about.

A small suggestion, if I may … specific to Thursday's experiment ^^^

You might reduce the 'variables' considerably, by cutting your offset pentagon on a plate of material, rather than a bar … essentially making the workpiece 'rigid' and thereby focussing attention on the effects of eccentric mounting.

Hope that makes sense

MichaelG.

[ChrisHParticipant @chrish]

Iain and Dave – I too have a Warco HV6 RT. A quick query.

If your table is securely mounted on the mill either horizontally or vertically, and the two RT table clamps are left slack, do your tables rock up and down, or side to side, as the case may be? Or is there little discernible play? (What is normal, what should one expect?)

I ask as mine does, (was wondering what I could do about it), it's worse – or more noticeable – when mounted vertically as in Iain's OP as gravity then only aggrevates the situation, and wondered also if that could be affecting the 'run out' problem? When I tighten the clamps things firm up, how much does it make it better I am not sure, not done the detailed checks yet, but there are times when you need to rotate the table when you are milling the job, not much use if it then wobbles about a bit, defeats the object somewhat.

Chris

I now seem to have found another checking/fixing task to do in the shed involving a mill and a rotary table……..

[JourneymanParticipant @journeyman]

Iain, the black plate on the underside simply bears on the body casting to prevent table lift. The combination of four cap screws and four grub screws adjust the clearance. If you loosen all the grub screws and tighten the cap screws the table will lock up! It is an excercise in patience to adjust the plate so that the table turns smoothly with no appreciable lift. I took my 4" Vertex apart when I motorised it. Everything is fairly crude inside, no bearings as such just cast iron to cast iron faces. Picture below shows some of the parts:-

The critical measurements would seem to be the flatness of the base which also needs to be at 90deg to the end when used vertically and the parallelness (is that a word) of the top to the bottom. I don't think any of these are really adjustable by the user, save with a surface grinder, it is more a matter of making allowance when setting up / maching a part. It also occurs to me that whatever is in / on the rotary table is at the end of a long chain of things that can be out of true. i.e. R.T. square to mill table, vertical to mill table any swarf under the table? this of course assumes that the mill itself is absolutely "in tram" in all directions. Loads of variables which all add up if just slightly out. Me I'll just work to the nearest mm

John

Edited By Journeyman on 29/03/2017 10:32:03

[SillyOldDufferModerator @sillyoldduffer]

Just a quicky as I have to hit the road in a mo.

Iain, "Wow! That's a bit too professional for me …"

You are too kind. What I'm trying to do is provide repeatable evidence. Without evidence, my opinions might just be prejudice. As I'm a self-taught beginner, I find it best to explain what I'm doing in some detail so that others can spot my mistakes. I've learned a lot on the forum. I'm sure wading through my wafflings isn't to everyone's taste, so thank you to those who have the stamina.

ChrisH, "If your table is securely mounted on the mill either horizontally or vertically, and the two RT table clamps are left slack, do your tables rock up and down, or side to side, as the case may be? Or is there little discernible play? (What is normal, what should one expect?)"

Yes, my table improves considerably when the clamps are tightened. The improvement is most noticeable with the table in the vertical position: I can see the crack between the turntable and the body disappear when the clamps are locked. In the horizontal position with a heavy 6" chuck mounted, it's not noticeable.

I always lock the turntable before taking a cut if possible. When using the table to move the work against a cutter, I nip the clamps short of an actual lock to reduce the unwanted movement.

I've not had my table apart to see if anything can be done. John's post (Journeyman) is much more helpful than anything I could say!

Time to go!

Cheers,

Dave

[Martin ConnellyParticipant @martinconnelly55370]

I know you have a rotary table and are using it for this task but it seems over the top for simply rotating something to 5 different positions. I would use my Stephenson's indexing head and ER32 collets (ARC Eurotrade sells them, they step in 1° intervals) for this type of job and as JasonB suggested support the workpiece near the working point with vee block, engineer's jacks, back plates or a suitable combination of them. Lightly clamped in a screw jack vee block would be my first choice. That way run out has no effect on the machined result.

You can use the same method with a rotary table just using it to rotate to the 5 positions and securing the work piece like you would for any other milling job to ensure a consistent result for each face.

Martin C

[Iain DownsParticipant @iaindowns78295]

Finally back at work at the same time as the chap who commissioned the pentagon.

It turns out that it's a 'security' spanner for attaching bike (pedal) wheels. Rather pleasingly, despite my diatribes on the errors involved, the part fits in the socket. A little too loose, actually, but that's just bad workmanship.

Iain

[Martin ConnellyParticipant @martinconnelly55370]

Here is what I described a couple of posts back. Using a spin indexer for simple dividing with whole degree spacing. Clamping the end in a vee on a screw jack I set the depth of cut to 1mm as this would leave a small untouched surface opposite each face. This would take away variations due to burrs on the apex. The resulting dimensions from flat to apex varied from 11.02mm to 11.05mm.

Martin C

[ChrisHParticipant @chrish]

I think between you, John (Journeyman) and Dave (SillyOldDuffer), you have answered my query. It would appear that the grub screws need to be adjusted to take out all play before the capscrews are locked solid on the wee plate underneath the RT and then hopefully the RT will run true. I hope for some shed time tomorrow – I will investigate, but thank you to you both for your comments they have helped me, and apologies to Iain if I hijacked his thread a little!

Chris

[David Standing 1Participant @davidstanding1]

Personally, if the workpiece is unsupported at the other end (and better practice even if it is), I would never use a rotary table just being clamped to the mill table by the base, even with a clamp on the back as well, as there are lots of leverage forces at play.

As well as the RT being clamped to the mill table, I would use a big angle plate or box big enough to also reach the top flange mount of the RT and clamp it there, as well as to the table.

Supporting the workpiece at the other end would probably cure most of the issues, but it still offends my engineering eye to see a RT just clamped near the table like that.

Not a criticism as such, just an observation

[Tony Pratt 1Participant @tonypratt1]

David,

You are spot on!! Again not a criticism but an observation.

Tony

[SillyOldDufferModerator @sillyoldduffer]

Posted by David Standing 1 on 29/03/2017 23:03:45:

Personally, if the workpiece is unsupported at the other end (and better practice even if it is), I would never use a rotary table just being clamped to the mill table by the base, even with a clamp on the back as well, as there are lots of leverage forces at play.

As well as the RT being clamped to the mill table, I would use a big angle plate or box big enough to also reach the top flange mount of the RT and clamp it there, as well as to the table.

Supporting the workpiece at the other end would probably cure most of the issues, but it still offends my engineering eye to see a RT just clamped near the table like that.

Not a criticism as such, just an observation

Excellent! I hadn't thought of doing that.

Reinforcing the sense of David's suggestion, although I successfully jammed a rear clamp into the groove at the back of the table, I don't think the slot is intended for that purpose. It's only about 5mm deep and using it didn't feel quite right.

The only down side is that I don't have a box or angle big enough to reach the top flange. On no! Another new entry on my ever growing 'to-do' list.

Many thanks,

Dave

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 30/03/2017 10:20:54:

Reinforcing the sense of David's suggestion, although I successfully jammed a rear clamp into the groove at the back of the table, I don't think the slot is intended for that purpose. It's only about 5mm deep and using it didn't feel quite right.

That is, almost certainly, what the groove is for. Many toolroom vices have similar clamping slots, juts use a clamp with a tapered nose that fits right in to the groove.

Neil

[David Standing 1Participant @davidstanding1]

Posted by SillyOldDuffer on 30/03/2017 10:20:54:

Posted by David Standing 1 on 29/03/2017 23:03:45:

Personally, if the workpiece is unsupported at the other end (and better practice even if it is), I would never use a rotary table just being clamped to the mill table by the base, even with a clamp on the back as well, as there are lots of leverage forces at play.

As well as the RT being clamped to the mill table, I would use a big angle plate or box big enough to also reach the top flange mount of the RT and clamp it there, as well as to the table.

Supporting the workpiece at the other end would probably cure most of the issues, but it still offends my engineering eye to see a RT just clamped near the table like that.

Not a criticism as such, just an observation

Excellent! I hadn't thought of doing that.

Reinforcing the sense of David's suggestion, although I successfully jammed a rear clamp into the groove at the back of the table, I don't think the slot is intended for that purpose. It's only about 5mm deep and using it didn't feel quite right.

The only down side is that I don't have a box or angle big enough to reach the top flange. On no! Another new entry on my ever growing 'to-do' list.

Many thanks,

Dave

I've got a WM18 and an HV6 RT, but I have never used it on its side. If I ever do, I might need a big angle plate or box too! .

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Journeyman on 29/03/2017 09:58:55:

Iain, the black plate on the underside simply bears on the body casting to prevent table lift. The combination of four cap screws and four grub screws adjust the clearance. If you loosen all the grub screws and tighten the cap screws the table will lock up! It is an excercise in patience to adjust the plate so that the table turns smoothly with no appreciable lift. I took my 4" Vertex apart when I motorised it. Everything is fairly crude inside …

.

Thanks for posting the photos … it's always interesting to see the guts of these things.

I was surprised to see that they use four of each screw [given that three of each would be both technically superior and 25% cheaper]; but I'm sure John Stevenson will be pleased.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 30/03/2017 10:27:42:

Posted by SillyOldDuffer on 30/03/2017 10:20:54:

Reinforcing the sense of David's suggestion, although I successfully jammed a rear clamp into the groove at the back of the table, I don't think the slot is intended for that purpose. It's only about 5mm deep and using it didn't feel quite right.

That is, almost certainly, what the groove is for. Many toolroom vices have similar clamping slots, juts use a clamp with a tapered nose that fits right in to the groove.

Neil

I was going to question Neil's comment using the photo below to show that the vertical part of a 'T' shaped slot couldn't possibly be intended to take a clamp.

On closer inspection, I think I'm wrong . The vertical slot has a construction hole in it and there's a matching hole at the top of the table. The holes have been protected by shallow slots, one of which happens to be part of the 'T'.

Apart from being used to take a clamp, I can't think of any purpose of going to the trouble of cutting the slot forming the top of the 'T'. Score so far Neil: 1; Dave: 0

After removing the rear clamp I put a DTI on the chuck. Then with 250mm of 3/4" steel pipe in the nose as a lever, I found the following movement:

• Locking clamps undone: 0.12mm
• Locking clamps applied: 0.06
• Rear clamp and Locking clamps applied: < 0.02

In all cases the table stiffens up considerably after the initial strain has been taken up. Even so, it emphasises the need to fix everything firmly, particularly when cutting at any distance from the chuck.

My education continues! At this rate I shall be employable in 2040.

Cheers,

Dave

Edited By SillyOldDuffer on 30/03/2017 11:25:55

Edited By SillyOldDuffer on 30/03/2017 11:27:03

[JourneymanParticipant @journeyman]

Dave, I think you will find that those slots are for fitting keys to align the rotary table to the mill table without the need for measuring or setting up. Clip from the Grizzly/Vertex manual:-

** Manual Link **

John

Edited By Journeyman on 30/03/2017 11:54:52

[David Standing 1Participant @davidstanding1]

Posted by Journeyman on 30/03/2017 11:52:03:

Dave, I think you will find that those slots are for fitting keys to align the rotary table to the mill table without the need for measuring or setting up. Clip from the Grizzly/Vertex manual:-

** Manual Link **

John

Edited By Journeyman on 30/03/2017 11:54:52

You realise that just made Dave now unemployable until 2090? .

[SillyOldDufferModerator @sillyoldduffer]

Posted by David Standing 1 on 30/03/2017 11:55:42:

Posted by Journeyman on 30/03/2017 11:52:03:

…

.John

Edited By Journeyman on 30/03/2017 11:54:52

You realise that just made Dave now unemployable until 2090? .

2090? I doubt it, every time I think I know what I'm on about, it turns out to be a half-understanding. On the bright side, thanks to Journeyman, the score now is: Dave:1, Neil 0!

The manual that came with my HV-6 doesn't mention those slots at all. Hurrah for Grizzly!

Dave

PS Earlier today I looted the details of how to connect a NEMA stepping motor to an RT from Jpurneyman's website. Given the number of people on the internet, is us connecting twice on the same day statistically likely or not?

[Author]

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