Author Topic: Making a Rotary Table  (Read 27199 times)

Offline Fergus OMore

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Re: Making a Rotary Table
« Reply #25 on: September 07, 2014, 03:21:29 PM »
Agreed Matt. Frankly, I have a number of rotary tables- some professionally made and others home made from assorted metals. Only one has ball races and that is on a Clarkson tool and cutter grinder.

It suggests that this idea of needing fancy bearings in model making somewhat 'over engineered'

Regards

Norman

Offline awemawson

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Re: Making a Rotary Table
« Reply #26 on: September 07, 2014, 03:26:33 PM »
If you recall the pictures of when I was rebuilding that Nikken rotary table unit as a 4th axis for my CNC mill it has rollers for table down force and rollers for side thrust:

http://madmodder.net/index.php/topic,9439.0.html

I suspect though it was built to withstand far higher forces than you will generate with your splendid beast
Andrew Mawson
East Sussex

Online NormanV

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Re: Making a Rotary Table
« Reply #27 on: September 07, 2014, 03:34:19 PM »
Yes, I realise now that a PTFE washer in the lower position would be daft, I will use a steel one. I like the idea of using PTFE under the table, I checked on Wikipedia and it gives a yield strength equivalent to 3,300 PSI. It seems unlikely that my usage will get near to that.
Andrew, I think that your rotary table is probably a bit big for my milling machine! I think that I was trying to overengineer it, for my light usage I think plain bushes and washers will do the job.

Online NormanV

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Re: Making a Rotary Table
« Reply #28 on: September 08, 2014, 08:11:48 AM »
I have bored the holes for press fitting the bushes for the worm. I had originally planned to bore it by mounting on the tee slotted table on my lathe and boring it with a boring bar between centres. Unfortunately I had nothing to use as packing to raise it to centre height, so instead I mounted it in the four jaw chuck. I was concerned that it would be a bit precarious but I had no problems. When boring the hole nearest to the chuck the boring bar flexed rather alarmingly but by taking light cuts and several at the same setting it turned out well.

Online NormanV

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Re: Making a Rotary Table
« Reply #29 on: September 08, 2014, 08:13:50 AM »
I also made the bushes to mount the worm, when pressed in the worm rotates freely and without any play.

Offline vtsteam

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Re: Making a Rotary Table
« Reply #30 on: September 08, 2014, 08:19:58 AM »
Coming along nicely, Norman! :clap:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline mattinker

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Re: Making a Rotary Table
« Reply #31 on: September 08, 2014, 01:00:43 PM »
I'm really enjoy your threads!

Regards, Matthew

Online NormanV

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Re: Making a Rotary Table
« Reply #32 on: September 08, 2014, 06:04:45 PM »
Thank you Steve and Matthew. Tomorrow I'll be working on the main spindle. Trouble is I don't have a piece of steel the right size so I will have to try to work out another solution.

Online NormanV

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Re: Making a Rotary Table
« Reply #33 on: September 09, 2014, 10:49:53 AM »
The main spindle is done. I just made it from two pieces of steel bolted together. I may cut a keyway to engage with the worm wheel but it is quite a snug fit and may not be necessary.

Online NormanV

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Re: Making a Rotary Table
« Reply #34 on: September 10, 2014, 02:27:56 PM »
I cast the table today, despite my misgivings I used charcoal again. This time it was much more successful, it only took an hour to complete the melt and used half as much charcoal. I had a stronger air blast and that seemed to do the trick.
I've also machined it all over and it is now mounted on the spindle.

Offline Arbalist

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Re: Making a Rotary Table
« Reply #35 on: September 10, 2014, 04:01:36 PM »
Looking good again Norman. As an aside, I've noticed in some of your builds you use pozidrive countersunk screws quite a bit, may I suggest you seek out some Torx versions next time you need to stock up on fasteners as the drivers don't cam out like they can on cross point screws.

Offline Manxmodder

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Re: Making a Rotary Table
« Reply #36 on: September 11, 2014, 07:39:36 AM »
Good work Norman,coming along nicely.

I would second Arbalist's suggestion on Torx head screws as they really are a far better engineered screw driving head than any of the cross head variety.......OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Online NormanV

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Re: Making a Rotary Table
« Reply #37 on: September 11, 2014, 08:34:23 AM »
I agree with both of you that pozidrive are not particularly good. I am not familiar with Torx but my first choice would be Allen socket head screws. Unfortunately pozidrive is what I have and that is what I will use until they are finished.

Offline Arbalist

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Re: Making a Rotary Table
« Reply #38 on: September 11, 2014, 11:26:47 AM »
I try to avoid socket hex countersunk screws in the small sizes as I've had the sockets round off. This has required me to drill out a few fasteners. I believe the problem is that sometimes countersink screws can self tighten with vibration as I certainly haven't over tightened them.

Just one random supplier of Torx screws:

http://www.accuscrews.co.uk/32-hexalobular-countersunk-screws

Offline philf

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Re: Making a Rotary Table
« Reply #39 on: September 11, 2014, 12:22:22 PM »
I try to avoid socket hex countersunk screws in the small sizes as I've had the sockets round off.

Arbalist,

I second that. When I built a vertical head for my Aciera many years ago I did a trial assembly of a bearing retainer/seal housing with M6 countersunk socket screws. Two minutes later I couldn't get them out with the correct 4mm Allen key which ended up rounding off. I resorted to drilling the heads off. I used slotted screws in the end. The same can apply to button headed socket screws which have smaller sockets than a normal cap head screw.

Phil.
Phil Fern
Location: Marple, Cheshire

Online NormanV

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Re: Making a Rotary Table
« Reply #40 on: September 12, 2014, 03:12:40 PM »
It's not been a good day today. I bored the top plate to take a steel bush for the spindle to run in. I then started on the bush, I managed to make the OD undersize and the ID oversize! So I started again, I was lucky to find that I had a piece of steel just a few thou oversize, but I am fed up with having to hacksaw through 40mm dia. bar (next project, power hacksaw)
I completed the bush correctly this time, a press fit into the top plate and, at the moment, a tight fit on the shaft. Tomorrow I will lap it to fit.


Online NormanV

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Re: Making a Rotary Table
« Reply #41 on: September 13, 2014, 06:04:01 AM »
I finished lapping the bush and pressed it into the top plate and then drilled and tapped the holes for attaching the top to the main body.

Online NormanV

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Re: Making a Rotary Table
« Reply #42 on: September 13, 2014, 06:07:28 AM »
I have used a PTFE washer under the table to reduce friction. I scored the outside circle with my dividers and then snapped the waste material off. It gave a rather ragged edge so I tried cutting it with a scalpel, it cut very easily and gave a much better edge. I had to resort to sanding the outer edge to smooth it.

Online NormanV

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Re: Making a Rotary Table
« Reply #43 on: September 13, 2014, 06:11:38 AM »
Then the exciting part! First assembly, it all fitted together nicely. You will notice that I have left the top oversize. This was to enable me to adjust the gears to be free of backlash without the necessity of ultra precision marking out and cutting, this has worked well. The next job is to dismantle it and trim the ends.

Offline awemawson

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Re: Making a Rotary Table
« Reply #44 on: September 13, 2014, 06:50:07 AM »
 :thumbup: All looking very nice Norman  :thumbup:

Are you going to mill Tee slots or drill and tap a matrix of holes as hold downs?
Andrew Mawson
East Sussex

Online NormanV

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Re: Making a Rotary Table
« Reply #45 on: September 13, 2014, 07:07:24 AM »
I would like to machine tee slots but am a bit nervous of it. I might try first on a piece of scrap. Drilled and tapped holes would be easier plus I wouldn't need to buy or make a cutter.

Offline awemawson

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Re: Making a Rotary Table
« Reply #46 on: September 13, 2014, 08:04:27 AM »
If you place tapped holes where you would have put Tee slots, then you have the option of still making the slots at a later date  :ddb:
Andrew Mawson
East Sussex

Online NormanV

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Re: Making a Rotary Table
« Reply #47 on: September 13, 2014, 09:05:23 AM »
Good idea Andrew!
The next job I attempted today was the locate the worm wheel on the shaft. Ideally I would cut a keyway in the shaft to match the one in the gear, I don't yet have the collet to fit the cutter required so I thought that if I put a short grubscrew in the shaft it would locate in the slot. This I did and the gear slipped on beautifully and was fixed in position on the shaft. Unfortunately it makes it impossible to assemble due to the curved face of the worm wheel!
Plan two is to drill a hole axially into the end, half in the shaft and half in the wheel and pin it, I've done it before to lock loco wheels onto their axle so I know it will work.
Plan three is to be patient and wait until I get the correct size collet!

Offline awemawson

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Re: Making a Rotary Table
« Reply #48 on: September 13, 2014, 09:41:46 AM »
Norman,

make a temporary collet on your lathe. Chuck up a bar of a size that you do have a collet for, drill suitably for the cutter, fix with a grub screw. Take light cuts. OK it won't be as accurate as a collet, but should suit the job in hand, especially if your cutter is narrower than the slot and you are cutting in two passes, one each side.

Alternately you could 'shape' the key way in the lathe using a parting tool held sideways, or with a bit of hss suitably ground. Youtube abounds with examples :)
Andrew Mawson
East Sussex

Online NormanV

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Re: Making a Rotary Table
« Reply #49 on: September 13, 2014, 03:00:55 PM »
Andrew, you make me feel a bit foolish, I seem to be looking for the problems that don't exist. I did exactly what you suggested and made a holder for the cutter to fit in a larger collet. The whole thing took about 30 minutes and I ended up with a proper bit of engineering. Thanks.