What have you invented?

[Stustoys]

Hi Bob,

I think I've confused you. When I said the Tee nuts were slipping I mean the fixed clamp(the black part in the pictures) is slipping. In fact the tee nut may not be moving at all as we are talking about a very small movement, about 0.006" before the clamp bottoms, I'll check. I'd like to be able to measure the force involved as when tightening the bolt the needle of a 0.0001" dti goes around at about the same speed as the allen key so roughly 2mm of vertical movement of the clamp would equal about 0.2mm movement of the fixed clamp.

Stuart

[RayG]

Hi Stuart,

I can understand why that clamp moves... after all something has to, you wouldn't expect the material to deform by that amount. that just proves how much clamping force there is. I'd say it's a success!

On another note, I bought a vacuum table on ebay last week, one of these eBay Australia: Buy new & used fashion, electronics & home d it's for clamping flat non-magnetic stuff on the surface grinder. I'll let you know how it goes, but I hoping 15 pounds per square inch should clamp nicely.

I'll need to set up a coolant trap before the vacuum pump..

Regards
Ray

[Stustoys]

Hi Ray,
Yeap something has to move. I trying to think of a way to do a rough crush comparison. Something like two pieces of alum MIG wire squeezed between metal plates by the clamp and then repeating the wire squeeze in one of my milling vices to see just how hard you need to wind to crush them about the same. Shame I have no alum MIG wire. Would copper wire do? I guess I can try it and see easy enough.

The table looks cool. Never seen one used on a grinder
You have a real vac pump?
If you get anything like a vacuum is a coolant trap going to work?
I wonder what volume you need to pull if you only have part the table covered? or is the idea to cover as many holes as you can with scrap?
Can you fix it to your magnetic table?
14.7psi

Stuart

[citybook]

Hi Stuart,
I think there is a problem with trying to anchor the clamp with one T bolt.

How about something like this ?

Cheers,
Bob

[Stustoys]

Hi Bob,
I had thought about two tee nuts but that limits you to clamping square to the Tee slot. I could add extra plates but I'm not sure they are necessary, as Ray said, its going to move somewhere. It seems that both fixed clamps are moving.

I cut some 3/4" lengths of 0.70mm copper wire and squeezed two between the step blocks you can see on the right in the pictures and the fixed clamp you cant see. The wire came out at 0.50mm. I then put two the same length in my hydroloc vice and did it up pretty tight. They came out the same or just a little bigger. So I seem to have plenty of clamping force and I can double or triple up. But a vice isn't going to "slide".

I guess it comes back to what work you want to do with them. I'd think mostly they would be used to facing cuts.

Stuart

[RayG]

Hi Ray,


The table looks cool. Never seen one used on a grinder
You have a real vac pump?
If you get anything like a vacuum is a coolant trap going to work?
I wonder what volume you need to pull if you only have part the table covered? or is the idea to cover as many holes as you can with scrap?
Can you fix it to your magnetic table?
14.7psi

Stuart

Hi Stuart,

Been away for the day, yes I have a "real" vacuum pump, it's a multistage RobinAir, the place that sells the vacuum tables also sells a coolant trap, but I've got a vacuum chamber that is used for degassing plastics and all I need to do is run a hose from that to the table, when it's sealed and running, there won't be any coolant getting into the vacuum side anyway, but the little bit that will get in accidentally needs to be stopped from getting into the pump.

I'm going to bolt it on a steel plate and that goes on the mag chuck.

I had a nice find on ebay, a 12"x8" compound magnetic sine table, it's a Robbins, who are now owned by Suburban, got it for a $450 inc shipping, you wouldn't want to know the new price!

eBay Australia: Buy new & used fashion, electronics & home d

Note to self, stay off ebay...

Regards
Ray

[Anorak Bob]

That's a real nice bit of gear Ray. You have to love Yank names, Omer!

It will be interesting to see how long you have to wait for it to arrive. I'm into week 5 for a Dumore part. Bryan has been waiting longer for something he purchased from the States.

Bob.

[RayG]

Hi BT,

Thanks, Omer is a great name.. I've had over 4 weeks wait for stuff recently, so I'll be expecting it in 4-6 weeks... maybe.

When I looked at it I suspected it might not be magnetic, although the description and the manual they picture say it is, the pictures don't look like it. First there is no sign of laminations, second there's no handle, and third it doesn't look deep enough. I won't be dissapointed it it turns out that it's not a mag chuck, I really want the compound sine setup.

Regards
Ray

[Stustoys]

Hi Ray,
How does a coolant trap work in a vacuum?wont the water just evaporate? hmm but the oil wouldnt right?(sorry thinking aloud lol)
I was surprised to read that it will work with a shop vac.

That table sure is pretty. There was a non magnetic one over here not long ago that went for almost that much and I'm not sure it wasn't "home" built
Did you get some gauge blocks to go with it?

Stuart

p.s. I think you're right about it not being magnetic. Thirdly tapped holes
"USAF" hey

[RayG]

Hi Ray,
How does a coolant trap work in a vacuum?wont the water just evaporate? hmm but the oil wouldnt right?(sorry thinking aloud lol)
I was surprised to read that it will work with a shop vac.

That table sure is pretty. There was a non magnetic one over here not long ago that went for almost that much and I'm not sure it wasn't "home" built
Did you get some gauge blocks to go with it?

Stuart

p.s. I think you're right about it not being magnetic. Thirdly tapped holes
"USAF" hey

Hi Stuart,

Here's the liguid seperator that they sell to go with that table, they have a pretty fair range of vacuum clamping stuff. Liquid Separators

I don't have gauge blocks, it's on the list, but all the ones I liked are too expensive.. (familiar story)

Just going back to the clamps you are making, the amount of clamping force you are getting must be huge. I wonder if you could limit the force by making the angled part from some softer material like copper or aluminium.

Regards
Ray

PS I liked the USAF too!

[Stustoys]

I don't have gauge blocks, it's on the list, but all the ones I liked are too expensive.. (familiar story)

They are on my list to, but I dont really have a good excuse to buy them. Now you do.

Yes its seems I over did it with the 1/2 UNC on the clamp, I only used that because thats the size of my clamp set. I have some 50x40mm Alum bar I could try making a clamp out of that. I have a couple of other ideas I'll try. I could just make a short allen key lol

Stuart

[jhovel]

Here is a collection of photos I've found over the years for "future projects" and to recognise if I saw one at a garage sale or market:
(The single piece one is called a 'toe clamp' and can be supported against a the head of a short bolt in a T-nut to execrt more force.)

[RayG]

Hi Joe,

Thanks for those pictures, I like the toe clamp, I think that shape would work nicely with Stuarts idea.

The step on the bottom would automatically limit the force....

Simple to make as well.

Regards
Ray

[jhovel]

I guess the last image most closely approximates your idea Stuart?

[citybook]

From my point of view we are missing the point here a bit.

The toe clamp (left pic) works by pressing down on the top of the work, and it's fixing is in tension - works well.

A problem with this is that you can't machine the area where the clamp is pressing on the work - ie. the top surface. You have to muck about moving the clamp to somewhere you have already machined and then make another pass to clean up where the clamp was before - and hope the work didn't move when you undid the clamp.

This one on the right is a pinch clamp - it works by pressing on the side of the work, and the fixing is in shear.

One reason for using it is that it does not obstruct the top surface of the job.

And this is what the question was about.

The clamps both Stuart and Dave came up with are pinch type clamps.

Characteristics of this sort of clamp is they develop a lot of force over a short range - they don't have very good contact with the work - and the fixing is in shear.

The last bit - ie. shear load on the fixing - is the reason most of the pics above that are pinch clamps have two T bolts.

Personally, I don't want a clamp that is "going to move somewhere" - an airborne workpiece can be a very character building experience.

Cheers,
Bob.