problem with rotary table

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problem with rotary table

This topic has 13 replies, 7 voices, and was last updated 8 October 2018 at 18:18 by IanT.

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4 October 2018 at 17:31 #374531
geoff walker 1
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@geoffwalker1
I recently bought a mini rotary table. see photos

Today I was milling a curve in the aperture of engine frame.

My problem is that with the set up I had when I tightened the nuts the table became very stiff and it was really difficult to turn the handle on the table.

As you can see i have brass tee nuts, 4mm thread, which accept 4mm studding. the bar which goes across the frame is 1/4" m.s.

The more I tightened the nuts the stiffer the table. It feels like the tightening is distorting the table and thus creating unwanted friction between the table and base. That to me is illogical but I'm stumped for any other answer.

Any thoughts Guys
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4 October 2018 at 17:31 #9357
geoff walker 1
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@geoffwalker1
4 October 2018 at 17:35 #374534
John Rudd
Participant
@johnrudd16576
If you place a clock gauge on the rotab and with the base on the mill as a reference, watch the clock as you tighten the clamps….if the pointer moves….
4 October 2018 at 17:50 #374537
SillyOldDuffer
Moderator
@sillyoldduffer
I can't account for that, but two thoughts:
- check that the studding can't turn beyond the base of the brass T-nuts and press on the base of the table as you tighten up.
- A nastier possibility is that the table has been damaged cutting the curve. Quite a few reports of bigger tables than yours coming to a sticky end when being used that way on steel – the gears inside aren't all that tough. If all else fails, you might have to look inside.
Hope it's something trivial!

Dave
4 October 2018 at 18:31 #374551
JasonB
Moderator
@jasonb
Where do you have the packing pieces that are lifting the work off the table? you are less likely to distort the table if they are directly below the points where your 1/4" clamping plate is placed. I would usually put something over the whole area that won't hurt the cutter such as 6mm MDF or a bit of rigid PVC sheet.

Edited By JasonB on 04/10/2018 18:33:26
4 October 2018 at 21:31 #374575
IanT
Participant
@iant
Sounds a lot like the same problem that can occur when you tighten the T-nuts too much on a cross-slide Geoff (like a Myford for instance). The answer there (and perhaps to your rotary problem) is to make a sub-table. I have them for my lathes and mills – partly so I can attach things that don't normally fit the holes/slots – but also so I can really tighten work down to them (and sometimes to move work (& table) between machines without disturbing the work setting (by referencing the table).

I haven't made any for my rotaries yet – but if I had this problem with one – I think it would the first thing I'd try. They don't have to be anything fancy and are very useful once made.

Regards,

IanT
5 October 2018 at 07:35 #374604
geoff walker 1
Participant
@geoffwalker1
Hi All

Big thank you for all your replies, all of which are really helpful.

A little experiment last night revealed that clamping pressure on the outside of the rim causes the table to lock, when it's nearer the centre there is no problem. I set up a dial gauge as John suggested and you see the finger move as the table flexes, not much but enough to tighten it up. It's very frustrating, I'll have a good look at it this weekend.

Really like the idea of a sub table, I have one for my lathe cross slide, they are a good idea. It might help to even the load across the table

I'll report back on this one. Thanks to all again

Geoff
8 October 2018 at 09:22 #375029
geoff walker 1
Participant
@geoffwalker1
Hi All,

I have to say I was really disappointed with this little table of mine.

I didn't expect to have the problem I had. Having said that it was "cheap as chips" so I suppose you get what you pay for!!

Anyway I took Ian T's advice and made a small sub table. This is secured firmly by 4 screws nearer to the centre of the table. The underside of the sub table is relieved 3/4" in from the perimeter so no pressure is applied to the outer rim of the table.

No binding or flexing problems now and it should be ok for the work I have planned.

Geoff
8 October 2018 at 09:46 #375032
Michael Gilligan
Participant
@michaelgilligan61133
Glad to see that you've made it useable, Geoff

I do remain intrigued as to the original 'failure mode' though …

If you ever dismantle it, perhaps you could take a few photos to show the design, and the finish of any bearing surfaces.

Thanks

MichaelG.

Edited By Michael Gilligan on 08/10/2018 09:48:33
8 October 2018 at 13:27 #375060
geoff walker 1
Participant
@geoffwalker1
Hi Ian, Michael,

I do remain intrigued as to the original 'failure mode' though …

It's not really a failure as such Michael. The unit is generally well designed the action is very smooth with very little backlash. The problem as I see it is the outer rim of the table has very thin section whereas the inner part of the table has a boss underneath which stiffens it up. If you look at the set up in the earlier photo you can see that the engine frame is bearing down hard on the outer rim. This combined with the upward thrust of the tee nut is causing the rim to flex, not much, but enough to create friction between the table and the base. It's a design fault, if the outer rim was a little thicker I don't think there would be problem.

Geoff
8 October 2018 at 13:38 #375062
Michael Gilligan
Participant
@michaelgilligan61133
Posted by geoff walker 1 on 08/10/2018 13:27:19:

Hi Ian, Michael,

I do remain intrigued as to the original 'failure mode' though …

It's not really a failure as such Michael.

.

I was reluctant to use the term, Geoff … but couldn't think of a better one.

< For the defence > Whilst nothing broke, the device failed to perform as required.

MichaelG.
8 October 2018 at 15:40 #375078
IanT
Participant
@iant
That's a tidy job Geoff – and if it's now working to your satisfaction – I wouldn't worry further about it.

Regards,

IanT
8 October 2018 at 17:46 #375093
Pete Rimmer
Participant
@peterimmer30576
Posted by Michael Gilligan on 08/10/2018 09:46:53:

Glad to see that you've made it useable, Geoff

I do remain intrigued as to the original 'failure mode' though …

If you ever dismantle it, perhaps you could take a few photos to show the design, and the finish of any bearing surfaces.

Thanks

MichaelG.

Edited By Michael Gilligan on 08/10/2018 09:48:33

If bolting a part to the table makes it flex, then either the table or the part isn't flat. I'd be bluing the table up to see if it was pringle-shaped first off.
8 October 2018 at 18:18 #375097
IanT
Participant
@iant
A good point Pete – but even if the table is perfectly flat – the work usually isn't – and that's before you start applying clamps, straps & packing to attach that part to the table (or cross-slide etc) being used. Quite apart from the other benefits of using sub-tables – a lot of machinery designed for hobby use just isn't that "heavy-duty" in nature – sub-tables can help rectify this deficiency and reduce the possibility of causing damage (like to the T-slots for instance).

Regards,

IanT
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