Can I use Mitee-Bite Pitbull clamps to hold larger blanks for first ops?

[Garwood]

Redesigning some old fixtures for current machines and I want to get away from toe clamps on the first op if I can.

I make a few hundred parts annually from 1-1/4" to 3" thick sawed 6061 plate with an average size of 18" square. Smallest is 10"x10" and largest is about a 21" square.

How can I deal with sawing tolerance of the blanks VS the tiny clamping range of Pitbull clamps? I was looking at the #26050 1/4-20 sized knife edge clamps, but they only have a .024" range. My blanks are usually very close within a batch, but different batches can vary by .050" per side. If I go with the larger sizes of pitbull clamps my fixtures have to be thicker to hold the pocket and have enough thread for the SHCS. I don't want the expense or heft of 2" thick fixtures.

For the first op, using pitbull clamps, why do I see tons of fixture examples online where people use them on all sides of the blanks instead of using the pitbulls on one side to push the blank into a fixed cleat like a talon grip insert? Is it because the pitbulls have such a small stroke?

Thanks for any help!

 

[Garwood]

Just had another related thought-

Will a knife edge pitbull clamp work OK if it's skewed at a slight angle from the blank?

If so, I could mill the slot for a pitball clamp at a slight angle to my blank and tap multiple holes. That would give me an adjustable range without needing to make an adjustable carrier for the clamp or buying into one of their huge looking modular pitball clamp bases.

Thoughts?

 

[Vancbiker]

For plate work similar to what you describe, we used what we called mold rails. Basically a long bar about 2” square by varying lengths depending on what size machine they were built for. They had a full length T-slot and through holes to bolt to the table slots. Various stop blocks and clamp blocks were made to fit the T- slot. Some were made to use the pitbull clamps and talon grips. The infinite adjustability was super handy.

 

[Garwood]

That sounds pretty slick.

 

[Spruewell]

I would avoid putting pit bull clamps opposing each other.
It’s like having set screws opposing each other in a bushing. They are meant to push the shaft against the inside of the bushing to ensure maximum contact area and proper alignment. When the set screws are opposed to each other, it is only the points of the screws contacting the shaft allowing it to move and deform the shaft resulting in failure.
Another idea might be to have the ”fixed cleat” adjustable. Or perhaps even use the eccentric style clamps like the miteebite “knife edge” or “series 9” clamps as your fixed cleat

 

[Pattnmaker]

My most used fixture on my mill has 4 pitfalls on it using the ones with 3/8 cap screws. It's holding saw cut Plate 27.5"×23.5" or 27.5x19. Thickness varies from 5/8" to 7". So far it's worked well although they're not great for pulling all 4 corners down tight to the fixture. When I need to flip the plate for opp 2 that's not a problem . When height is critical and the plate is not getting flipped opp 1 is often drilling and countersinking hold down holes. These are not production parts however so I can typically spend more time making sure it's right. Not sure if one side Tallon grips would work better for pulling down.

 

[Garwood]

I would avoid putting pit bull clamps opposing each other.
It’s like having set screws opposing each other in a bushing. They are meant to push the shaft against the inside of the bushing to ensure maximum contact area and proper alignment. When the set screws are opposed to each other, it is only the points of the screws contacting the shaft allowing it to move and deform the shaft resulting in failure.
Another idea might be to have the ”fixed cleat” adjustable. Or perhaps even use the eccentric style clamps like the miteebite “knife edge” or “series 9” clamps as your fixed cleat

I was thinking similarly. Also, it would make sense to put a fixed cleat at the rear and pitbull clamps in the front so there's no reaching way into the machine.

I could make cleats with serrations like lathe chuck jaws have. Then mill those serrations into the fixture plate. I would have to use a pitch smaller than the range of the pitbull clamp I use though. That wouldn't be much of a serration.

 

[Garwood]

My most used fixture on my mill has 4 pitfalls on it using the ones with 3/8 cap screws. It's holding saw cut Plate 27.5"×23.5" or 27.5x19. Thickness varies from 5/8" to 7". So far it's worked well although they're not great for pulling all 4 corners down tight to the fixture. When I need to flip the plate for opp 2 that's not a problem . When height is critical and the plate is not getting flipped opp 1 is often drilling and countersinking hold down holes. These are not production parts however so I can typically spend more time making sure it's right. Not sure if one side Tallon grips would work better for pulling down.

That could be a whole new problem for me. Using toe clamps the plates are always sucked down flat on the first op. Some parts I only have maybe .020" cleanup material on a large surface so a lifted corner could mean the 2nd op doesn't clean up.

The more I think about my families of al plate parts and what you guys have said I think a modular setup kind of like what Kevin described could be best for me.

The 2nd op fixture is the same for all of the larger parts, All parts share a pair of counterbored bolt holes so I precisely bore the counterbores which locate on bosses on the flip.

If I make a 2nd op fixture plate smaller than the smallest width part I could use pitbull clamps on t-slot carriers. I want this to be fast changeover and I think I can do that if I have selectable spacers that go between the pitbull carriers and the side of the fixture plate. Setup sheet would name the spacers and where they go for each part. That could work and that would allow me to use the 1/2-13 size pitbulls without making my fixtures 2" thick.

Might have a worker here.

 

[MwTech Inc]

I just got the OK vise clamps 47100 and they are slick......lots of travel...bit pricy tho

 

[Garwood]

I just got the OK vise clamps 47100 and they are slick......lots of travel...bit pricy tho

I just do one plate at a time. I don't think those style of clamps will work for that since both sides move apart when you tighten the bolt.

The 1/2-13 size pitbulls have .075" travel which sounds workable for the size of parts I'm doing. And I like them having a 3/8" allen hex. I have a Dewalt impact gun that lives with a 3/8" hex key in it in the shop.

 

[MwTech Inc]

You can pocket them or simply put a stop on one side....I am using a pocket.
The little 47100 has .100 plus travel.

 

[Barbter]

As above - Okvise!
Sink them into a plate so the rear jaw is fully supported and the front can move full travel.
Sink them low enough so only say 4mm is protruding "up" - so you're only clamping on that amount.
Then put another pocket to the side and futher towards the fixed jaw for smaller stock.
Then repeat the same.
This allows one plate to hold many different widths.
You obviously only need a couple of the Okays and move them from position to position!