Bar clamp

Hi, can anyone tell me which is the best way of claiming a bar in a block of metal.

1. Slit the dark and use a bolt.

2. Use a 2 part cotter pin with bolt.

Thanks for any suggestions.

Tony S

Hello Tony

What's the application? Is it something you will adjust frequently or is it a fit and forget job? How much time and effort do you need to spend on making it?

Slitting the "dark" is a good way but be careful if using cast iron outer and the bar is a loose fit as it may break when you tighten it up.

There are quite a lot of ways of "claiming" the bar; I suppose the simplest was of clamping is a grub screw or similar. However unless you take precautions it will mark the bar, and it will also tend to force the bar slightly out of axial alignment - how much will depend on the clearance between the parts.

I imagine by your "2 part cotter pin and bolt" that you mean those split clamp affairs. They're good, and give excellent clamping. They don't mark the bar, but again they do tend to force the parts out of alignment as the grub screw does.

Another way is some kind of collet arrangement; tightening this up will give an excellent grip and maintain concentricity if you've made it correctly.

Tony,

I think you need to explain better. You may know what you want/mean but I, for one, am not sure.

As NDIY says, you need to be more specific.

How big are the parts?

Any thin walls, (specify )?

What materials are involved?

Will the clamp need to released frequently / regularly, or never again?

The answers to these questions will enable folk to give better advice, as to the method to be used

Howard

Hi, sorry I was not more specific, I was reading an article on on the G H Thomas Universal Pillartool ,the first castings were slit at the back to clamp the arms to the main post, this was changed to using the brass pad, the metal i will be using is mild steel, and the bore will be a good fit on the bar.

Both methods will clamp the bar, i was not sure which was the best option.

Tony s

Split cotter. The bored hole stays the same size with this meathod. Slitting invariably causes the hole to close up.

regards Martin

Split cotter holds fast and releases the bar fully when undone.
Best to machine the bore with the whole cotter in place, splitting it after boring or reaming the hole.

Emgee

Simpler to split it. If its mild steel and the hole closes up a whack with a hammer and fine chisel will wedge it open again.

If slitting, beware the work closing on the saw as it breaks through (the disc brake effect).

The split cotter method is the most elegant, is effective and avoids the problems of the fittings closing up as they stress relieve when slit. It also minimises the risk of cracking the castings.

If you don't fancy that, the threaded knob pressing a brass pad against the column is better than slitting, in my view.

Howard.

Can I speak up for the split castings. I made my UPT from Reeves castings decades ago, when the design first appeared in ME, and it's worked well that way. I use it quite frequently. In manufacture I suppose a casting is less likely to close on the slitting saw than BMS though

The sensitive drilling head, which followed a bit later, does use a split cotter since the split casting method isn't feasible, and that's good of course.

Thank you for your response to my query, I did like the response from hopper whack it with a hammer, spoken like a true engineer, lol .

I think I will use the brass pad (cotter).

Thanks again Tony s