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Thread: Swivel Base Revisited
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14th February 2012, 10:57 PM #1.
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Swivel Base Revisited
Not some Office Works chair but the base for my much laboured over dividing head mount.
I was not comfortable with the idea of a dovetail spigot and had been considering alternatives that might offer more security given my intention to mount the dividing head vertically. I located some photos of a partially dismantled universal dividing head on a French site and noticed that Schaublin used the same cam locking tee bolts to fasten that head to it's base, as they did on my simple dividing head. In the case of the heavier universal head, four tee bolts are used.
The "cam" is pretty simple and my intention is to replicate the originals by remachining M10 cap screws. The tee bolts are again simple and I think 4140 will work fine.
I was stumped for a while trying to work out how I might cut a circular tee slot. The conventional practice is an access hole from the underside for initially the cutter, then the tee bolts, typical mill vise fashion. In my case, I realised I couldn't install the tee bolts because of their barrel bodies. A removable "plug" as drawn below might be the answer. Another piece of 4140 secured with an M6 countersunk socket screw. I would prefer M8 but there is insufficient room. The location of the plug is in a position that I imagine would seldom engage a tee bolt.
Anyone notice any glaring or not so glaring omissions? And I'm not talking about the shabby drawings. I don't know how I left off the centre hole on both.
BT
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14th February 2012 10:57 PM # ADSGoogle Adsense Advertisement
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15th February 2012, 12:06 AM #2Dave J Guest
I had a good long look and think about any other ways, but I think you have come up with a good and possibly the only solution for those parts to be able to go into that T slot. Good thinking Bob.
Dave
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15th February 2012, 12:27 AM #3GOLD MEMBER
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Hi BT,
A couple of ideas,
Could you turn the tee slot in the lathe?
Would it be easier to turn a register onto the bottom of the piece that the dividing head mounts to that fits into the tee slot?
Couldn't you drill two holes from the bottom, one just big enough to pass the barrel bodies. Another much larger just into the slot to pass an over sized head tee bolt?(over sized enough that the centre of the bolt is pass one side of the barrel bodies hole before the head of the tee bolt clears the opposite side of the hole)
Stuart
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15th February 2012, 12:33 AM #4Mechanical Butcher
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A 2 piece T bolt, with the bottom part screwed to the top, would allow assembly from the bottom. It could also provide adjustment for the cam action. It would be bulkier, and some way of preventing the circular T bolt from turning once adjusted would be needed - maybe a nylon friction insert?
Jordan
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15th February 2012, 12:59 AM #5Dave J Guest
Going off the pictures Bob posted, it doesn't look like there is much room in the base for a larger T slot, and there is not much meat between the reduced shank part for the T bolt and the cam hole. Seems like it's a tight squeeze to fit it.
Someone posted pictures of a Taiwanese lathe a while back where they come with just holes in the T slot for the compound bolts to get in. They where having trouble with the T bolt chewing the edges of the cast out around the holes when set at that angle. At least with Bob's fix it would have the patch piece to give even pressure either side of the T bolt.
Dave
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15th February 2012, 06:46 AM #6Philomath in training
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The only alternate that I can think of at the moment is to make the interior of the T slot bit a disc and bolt it in with some SHCS after putting in the inserts. That notch and cover arrangement looks fiddly and if the T-cam were right under it, it probably would not secure much.
Another option is to have a hole in the top that the T can be fed into in the least popular place - say at 80 degrees to the main axis - how likely are you to ever want to position something there (and with symmetry you can mirror things so it does not matter if you did.)
Michael
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15th February 2012, 08:57 AM #7Distracted Member
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I like Michael's idea of a bolt on mushroom. You'd get 4 or even 6 nice big screws in and it would be very secure and uniform.
Edit: Actually he said disc and that's probably all you've got room for.
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15th February 2012, 11:53 AM #8.
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Dave, Michael, Jordan, Stu and Bryan, thank you for thinking about this.
The bolt down disc is a pretty simple solution. It needs to be able to slide aside to allow the tee bolts to be installed. The centre bolt would provide alignment of the two major components.
I had considered a two piece tee bolt but the present 5 x 20 base ( proposed nut) of the bolt would need to be thickened somewhat to provide reasonable thread engagement with the resultant thinning of the material below the tee slot. Then a locking device would need to be devised.
Stu, holiday over? A integral register is something I have to think about. It would prevent the upper section from being mounted directly onto the mill table should the need eventuate.
BT
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15th February 2012, 12:56 PM #9Dave J Guest
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15th February 2012, 04:03 PM #10Mechanical Butcher
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That's one way, or the other end could be threaded.
Another idea: One piece, but using a modified oval shape to engage the T slot. Its width narrow enough to fit through from the top, and its length and shape sufficient to provide adequate clamping area when rotated to its working position. The hole for the cam would be offset by an angle, such that when it's in the correct position so is the clamp.
Jordan
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15th February 2012, 04:47 PM #11.
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I'm working through the suggestions.
JP,
I made a skewable nut for my table adjuster and while it works well in that application, the amount of engagement available is a bit limited on this current project. I will explore the idea further though with a drawing. Here's the two part tee bolt. The thread would be M8. Loctite is easy but makes dismantling a problem. Maybe a M3 or 4 socket set screw with a brass pad might be a better option.
BT
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15th February 2012, 05:59 PM #12
Hi BT,
I don't have any better suggestions that those you've already got,
But I like Jordan's two part T bolt idea, instead of a locking screw, you could use loctite thread lock ( a little less permanent than loctite 401 )and mill a screwdriver slot on the bolt head.
Regards
Ray
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15th February 2012, 10:34 PM #13Mechanical Butcher
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A little locally applied heat destroys the Loctite bond.
It doesn't need to be so hot as to affect the metal parts.
I guess it's not as nice as a purely mechanical solution.
Or, what about a very wide slot, so the bolt doesn't need to have 3 diameters, only 2 with the top part large enough to engage the cam.
JordanLast edited by nadroj; 15th February 2012 at 10:40 PM. Reason: Addit
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15th February 2012, 11:06 PM #14.
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16th February 2012, 11:35 AM #15.
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Might be a plan
The non waisted tee bolt as per Jordan's suggestion. I now have to work on a way of holding the two major parts together whilst providing accurate rotation.
BT
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