T63 toolpost question

[Jonathan Coates]

Has anybody had luck with these? Mine is this one Model Engineering and engineering tools online from RDG Tools Ltd Home Page (Engineering Tools) Tel 01422 885069 /884605
If the link works, it should show the arrangement of the thing. My issue is that the cam bit doesn't turn enough to lock, however much you try to force it, and it pops off during parting off. Have any of you machining experts had luck in modifying one to actually be useful? It's a lovely bit of kit, all except for the fact that it doesn't work.
The way it works is that the locking post holds a piston arrangement through an eccentric such that when its open there is clearance to lift out the toolholder and change it for a different one. Quickly. Hence the name, I suppose. But the lock position doesn't turn the eccentric all the way round so that the toolholder is clamped by the eccentric being opposite the released position. In fact it doesn't get much more that 100 degrees of rotation and a big force on the tool pops it off. That allows the tool to drop and move towards the chuck, and that causes frustration.

 

[SmithDoor]

Has anybody had luck with these? Mine is this one Model Engineering and engineering tools online from RDG Tools Ltd Home Page (Engineering Tools) Tel 01422 885069 /884605
If the link works, it should show the arrangement of the thing. My issue is that the cam bit doesn't turn enough to lock, however much you try to force it, and it pops off during parting off. Have any of you machining experts had luck in modifying one to actually be useful? It's a lovely bit of kit, all except for the fact that it doesn't work.
The way it works is that the locking post holds a piston arrangement through an eccentric such that when its open there is clearance to lift out the toolholder and change it for a different one. Quickly. Hence the name, I suppose. But the lock position doesn't turn the eccentric all the way round so that the toolholder is clamped by the eccentric being opposite the released position. In fact it doesn't get much more that 100 degrees of rotation and a big force on the tool pops it off. That allows the tool to drop and move towards the chuck, and that causes frustration.

I first start using that type in 1970's. I switch to Aloris in 1970's.
It was not a bad tool post but the Aloris was smaller and for some work the was great advantage. I had one on SB 9A and America 20" .

Dave

 

[djc]

That is a Dixon-style toolpost.

The Indian copies of the originals can sometimes vary in quality - there are a lot of tolerances that have to be in line for the thing to work. Clearly you have one where the tolerances have conspired not to make it work.

As it has two cams, two pistons and two positions, try all combinations to see if anything improves.

If not, you either have to grind a little off the toolholders so they sit more deeply into the vees or alter or remake the pistons so the hole is a little further from the flange. Both options will allow the cam to turn further.

Whatever you do, make tiny adjustments until it works.

The risk you take is that the next batch of toolholders you buy may be thinner than the existing ones and thus the cam will travel too far before the tool is locked into position.

Perhaps enlarge the existing hole in the piston slightly towards the 'inside' of the toolpost block (wooden dowel of the correct diameter wrapped in abrasive paper). Another option is to thin down the flange on the piston.

Whatever you do, you need to establish a relationship between the amount of material removed and the change in angle of the clamping handle.

If you say it turns 100 degrees now, stick a 0.010" shim on the flange and see how much the angle reduces. That will give you some indication of the relationship between the amount you remove and the extra angle gained.

 

[BaronJ]

Hi Jonathon,

I got rid of my Dixon toolpost a long time ago and made a Norman Patent one. I also made a rear toolpost version to hold a parting blade. I made both tool holders the same bore size so that I can swap between them at will. Its far superior and more rigid. Its also quite easy to make, being mainly a turning job.

I have a drawing for the Myford size one if you or anyone else wants a copy.