Thread: Swivel Base Revisited

Not a dumb question Ray but a dumb answer from me. It was a case of monkey see monkey do. I copied Schaublin's cam.

I had a look in a couple of my books and found some simple and more complicated answers to your question. I will create a new thread with some photographed pages because there may be broader interest.

Barleese on the taper comparison.

BT

.. and the project being slipped into the Sulo bin.

I cut off the 20mm diameter base of the clamp and reduced the length of the waisted section by 0.005". With a new base secured by means of a M6 screw, I assembled the swivel base. Inserting the cap screw cam was a bit difficult. Then I realised why. The cam can only be installed with the clamp in the locked position , ie, top dead centre. Because I had a tiny amount of play, the cam did not pull the clamp up as tightly as it should have if it was fitting properly. Fitting properly would have meant that I would not be able to disassemble the two parts of the swivel base.

I will now make the tee clamps as 2 piece affairs, the same as the trial version. I will bore an access hole in the underside of the round base to facilitate installation of the 20mm diameter screw on component. I still needed to have the removable plug in to top to enable the use of the tee slot cutter which had a 1/2" shank. The tee slot is 10mm wide.

BT

Oh dear.......another way around this would be to machine the end of the cam down to 8mm and putting a bush in the end of the cam hole. Then it could be assembled at any point. An m6 bolt in tension should be plenty strong though, and much easier to implement.

I'd been thinking something along the lines of "why isnt the end smaller than the cam?" but I hadnt taken it to the "can't get it together" conclusion.
The holes for the cams are bored already correct?
With the M6 grub screw design, at least the cams cant fall out.

Stuart

Boys,

When the cap screw cam is tightened it's lifting the tee clamp up and pushing the 10mm diameter shank of the cap screw down. Working correctly, it would be jammed tight with little chance of removal. Reducing the diameter of the outboard end to less than 9mm wouldn't help me.

Schaublin's use of the cam operated fittings is somewhat different. They are installed in the simple dividing head body then the head is slid onto the tee slotted saddle with the cams obviously loosened off. Then they are tightened. I can't do that.

I had wondered why Schaublin counterbored and countersunk the holes in the clamps. Without the countersink the removal of the cam would be real tricky.

Live and learn.

BT

But*, if the outboard end of the cap screw was reduced to 8mm. Couldn't you insert it when the thingamajig was loose/open/on bottom.

Stuart


*at least as I'm seeing it in my head

I have just spent my quiet shower time thinking about how this all works (you try thinking about things like this whilst children are screaming....). I have wrapped my head around why it works with the dividing head and not for the base, but i'm with Stu, i can only see it working if the end of the cam is 8mm. !f the top of the hole in the t thingy is 1mm lower than the cam hole (when it is lifted up in the t slot) then the cam could be put in bottom dead center and you have 1mm of tightening range......in my head anyway.

I don't want you boys thinking you are orphans, I have been pondering this also.

Stepping the outboard end down to 8mm would mean there was the likelihood of the cap screw cam falling out if the swivel base was mounted vertically, one of the main reasons for undertaking the project.

I am now wondering if I have the thickness of the 20mm diameter base of the tee clamp too great. If it is too thick I won't have the 1mm play offered by the cam offset. That could well be the reason for being unable to remove the cam in any position other than TDC. If I had the full 1mm travel, I'm thinking that I should be able to remove the cap screw cam at BDC.

Should isn't does. More testing tonight.

BT

Originally Posted by Anorak Bob

Stepping the outboard end down to 8mm would mean there was the likelihood of the cap screw cam falling out if the swivel base was mounted vertically,

Well we agree on that
Though and extra groove in the cam bolt and a grub screw into said groove could fix that.

Originally Posted by Anorak Bob

If I had the full 1mm travel, I'm thinking that I should be able to remove the cap screw cam at BDC.

I'm afraid not BT*, as is, the cam bolt will only pass through the thingamajig in the fully up/locked (plus a little bit more) position.

Stuart

*As I'm seeing it.

HI Bob,
I have read and re-read this and I must be missing something.
Can you only insert/remove the eccentric pins in the TDC position?
Is your maximum clamping position only in the TDC position?
Would it be true to say that through 180 degrees rotation you go from maximum slack to maximum tight?
I would have thought that the pin could be removed when the eccentric pins were in anything other than the clamped position ie TDC hence the lead in/out chamfer.
I also would have thought that a rotation of less than 180 degrees would be the target for maximum clamping effect (assuming 180 degrees is your distance of rotation for maximum clamping effect and you have that at TDC)
I just know there is something staring me in the face that I have missed.

Phil

Hi Phil,
The cam area has a smaller diameter(9mm) than the bearings either side of it(10mm).
So the cam area cant lift the thingamajig higher than the bearings lift the thingamajig(when being inserted).
The position of the cam at TDC or BDC has no effect until the 10mm bearing has passed through the thingamajig.
Think about it using the shank of a bolt that doesnt have the cam machined on it. If the thingamajig is long enough that the bolt can be slipped in it then cant pull the thingamajig any higher to clamp. (though with the cam you would be able to slacken it off 1mm).

Stuart

*of course I could be wrong

Phil and Stu,

I went up to the shed and had a proper look at the original cam/tee clamp setup. It is not possible to remove the cap screw cam when the dividing head is mounted on the tee slotted saddle, both Schaublin's and my pretend version. Dismounted, the two components fall out. I guess that last thing you would want is for the cams to fall out when you have the dividing head set up in some weird position like in the photo below.

I don't think I have any choice other than to bore an access hole from the underside and to make the tee clamps two piece. But before I do that I will have a go with a thinner 20mm diameter base on the tee clamp.

BT

Hi BT,
The second one will be a piece of cake

Originally Posted by Anorak Bob

I don't think I have any choice other than to bore an access hole from the underside and to make the tee clamps two piece. But before I do that I will have a go with a thinner 20mm diameter base on the tee clamp.

You could machine the end of the cam bolts to 8mm and fit a bush to the base as Ewin said earlier(adding something to stop the cam bolts falling out). The only problem I see with your idea of two piece thingamajigs is that you must remove the base from the mill table to get at the bottom, though I'm not sure how that could be an issue as even if you couldnt remove the top of the swivel base from the bottom you can still remove the dividing head from the top..... right?
Your idea would also make adjusting the length of the thingamajigs easier than making them in one piece.

Stuart

Originally Posted by Stustoys

Hi Phil,
The cam area has a smaller diameter(9mm) than the bearings either side of it(10mm).
So the cam area cant lift the thingamajig higher than the bearings lift the thingamajig(when being inserted).
The position of the cam at TDC or BDC has no effect until the 10mm bearing has passed through the thingamajig.
Think about it using the shank of a bolt that doesnt have the cam machined on it. If the thingamajig is long enough that the bolt can be slipped in it then cant pull the thingamajig any higher to clamp. (though with the cam you would be able to slacken it off 1mm).

Stuart

*of course I could be wrong

Thanks Stuart. Painfully obvious now
Old Timers disease must be setting in

Phil