While learning to use my mini-mill, I came up with a question: is there any valid reason the most common hold-down straight slotted clamps are designed in such a way that you can almost never have two attachment points per clamp (that is, have two threaded pins at the opposite ends of the slot, with the part you are machining "positively" secured between them)? The slots and/or the clamps are usually not long enough... Say, you are working on a narrow square-section bar stock, like 1" wide. Why not have two dual-pin straps securing it at both of its ends? Wouldn't this be a much more reliable setup than having one threaded pin per clamp? Yes, I do know you can still hold it down with the regular clamps, with the 1 pin/clamp situation. I just don't see the point of preventing one from doing it as described above (though I'm sure I must be missing something)...
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Milling machine hold down
- Thread starter xyz07
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It is likely that you never get a good solid hold down with a bar and 2 studs. the pressure and flatness would have to be perfect, or one side will be loose and if the held part were to move toward the high side it would also get looser. You are much safer using the clamps as designed. For the same reasons it is also important to always have the outside of the clamp higher than the surface it is clamped to.
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Hi @xyz07,
If I understand your idea, you are thinking about a longer clamp that bolts down to two t-slots; one on either side of the work-piece.
Like a strap across the top.
Is that it?
I think @Flyinfool has one point; that if you tighten one side first or more than the other you could actually push the part sideways.
Another reason that the regular style clamps are probably the norm is that they can work more universally as you do not need access to both sides.
You can hold down a work-piece, or a vise, or a rotary table, or .........
I think if they were used carefully your style of clamps could work.
-brino
If I understand your idea, you are thinking about a longer clamp that bolts down to two t-slots; one on either side of the work-piece.
Like a strap across the top.
Is that it?
I think @Flyinfool has one point; that if you tighten one side first or more than the other you could actually push the part sideways.
Another reason that the regular style clamps are probably the norm is that they can work more universally as you do not need access to both sides.
You can hold down a work-piece, or a vise, or a rotary table, or .........
I think if they were used carefully your style of clamps could work.
-brino
I appreciate the comments. Brino - that's what I thought; if I have a square-section bar on my table, the dimensional tolerances shouldn't be a problem (I mean - how crooked that bar or my mill table can be?). I do see how uneven nut tightening could be a problem, but if it's roughly the same (say, I count the turns or even use a torque wrench) - shouldn't be that bad? I suppose my idea was inspired by a subconscious fear of "flying-bar-stock-in-the-face" sort of scenario
, but, beyond that, I could likely just end up spending less time securing pieces that only consist of right angles and attaching them in a more "positive" way.
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Your approach and the conventional hold-down method share one problem, which is that they limit where you can actually mill. You also can buy or make low-profile workholders that grip the sides of the work piece. I have found them useful for situations where I need to mill the entire top surface, or the work isn't compatible with a vise (like long stock). I made a fixture plate similar to this, and some low-profile holders that are bolted onto the plate. This arrangement can hold pieces that are quite long -- I used it to make a guide bar for my table saw (the slots are not standard width so I couldn't buy an off-the-shelf one). I step-milled it so I ended up with a guide bar that is 2 feet long, far more than the mini mill's X axis motion.
Harold Hall's web site shows a number of different designs for low-profile workholders. They are designed to be installed with conventional T nuts, so you don't HAVE to make a fixturing plate.
Harold Hall's web site shows a number of different designs for low-profile workholders. They are designed to be installed with conventional T nuts, so you don't HAVE to make a fixturing plate.
Thank you for the tips - having the entire surface of a work piece at my disposal would be great.
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One commercial source for low profile cam clamps is mitee bite:
https://www.miteebite.com/products/t-slot-clamps/
https://www.miteebite.com/products/t-slot-toe-clamps/
Apparently they are sold on amazon.
Clickspring on youtube has a short "Clickspring Clips" video on modifying a regular socket-head cap screw to have an an offset head just for such a clamp:
I believe you need to be a patreon supporter to see his entire video.
-brino
https://www.miteebite.com/products/t-slot-clamps/
https://www.miteebite.com/products/t-slot-toe-clamps/
Apparently they are sold on amazon.
Clickspring on youtube has a short "Clickspring Clips" video on modifying a regular socket-head cap screw to have an an offset head just for such a clamp:
I believe you need to be a patreon supporter to see his entire video.
-brino
- Joined
- Jul 29, 2014
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- 2,737
Holding a part in place adequately is frequently an opportunity for creativity. Anything goes. I have made a couple 12” steel straps with a 1/2” hole in each end, and occasionally use them to strap down some unusual part...I think this is what the OP is suggesting.
Yes; and I was quite disappointed by the fact that the straight clamps from one of those standard $50-60 sets have a slot that is not long enough to do that... (until I learned how to use them properly
, but still).Thank you - I will make sure to check it out.