Festool Clamping Element clamping problem

[Chelmite]

I'm using a couple of clamping elements to hold a board in place while I CNC it. The problem is that when I tighten the clamping element, it lifts the workpiece off the table. The clamping element is pushing the workpiece against another pair of semi-circular clamping element pads. I also tried it with the Festool bench dogs with the same effect.

Is there something I need to do to keep the workpiece on the table when I use the clamping elements?

 

[Svar]

You can use knobs that came with the elements to secure them from under the table. Having said that, clamping elements are poor option for CNC. You need something that firmly holds your material down.

 

[rst]

If the elements are too tight they will raise your piece

 

[cronor]

It doesn't really matter how much you tighten. The workpiece is lifted immediately. Also, tightening the clamp with the screws helps very little. Any better suggestions? It's quite annoying.

 

[Bob D.]

I don't have a CNC but from using my FT clamping elements on the MFT/3 or for that matter any clamping tool of that style I would never trust them to hold a workpiece securely for CNC operations.

Maybe if you were doing some light duty engraving or relief work or laser etching they would be OK, but with a router or spindle running at a few thousand RPM I think you're asking for trouble (as in injury), or a spoiled workpiece and/or damaged tool.

 

[Stone Message]

I made up some little clamping elements from Maple. They are screwed into screw inserts in the base board.

View attachment 1

Peter

 

[xedos]

It doesn't really matter how much you tighten. The workpiece is lifted immediately. Also, tightening the clamp with the screws helps very little. Any better suggestions? It's quite annoying.

A better suggestion is what Svar already said - use something else !

Peter has given you a roadmap.

 

[peter halle]

If you look at your clamping element you will see a tiny screw.  That can be used to adjust the clamping pressure.  That may help you out, but every situation is different.

Peter

 

[Cheese]

I agree with the others that something that will be CNC'd needs to incorporate a more robust fastening method than some simple side clamps. That's truly a recipe for disaster.  [scared]

However I was surprised that no-one seemed to be interested in suggesting solutions for this clamping issue when they weren't using a CNC. Surely there must be someone out there that has and HATES this issue and just wants to clamp parts to the bench without the edges of the part lifting.

So I decided to try a very simple test.
Photo 1...clamps placed on a MFT, the clamped material is held down by hand and the clamps are tightened.
There is .025"-.030" of space under the material.

[attachimg=1]

Photo 2...clamps placed on a MFT, the clamped material is held down by hand and the clamps are tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is .012"-.015" of space under the material.

[attachimg=2]

Photo 3...clamps placed on a MFT, the clamped material is held down by hand and a fender washer is added to the clamps and they are  tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is .002"-.003" of space under the material.

[attachimg=3]

Photo 4...clamps placed on a MFT, the clamped material is held down by hand and two fender washers are added to the clamps and they are  tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is less than .0015" of space under the material.

[attachimg=4]

And this is the side view. If you don't want to deal with the feeler gages, check it out yourself, just clamp an item down to the MFT, observe the .030" space under it and then place 2 fender washers on the Festool knob, tighten the knob and then observe the gap...next to nill.  [big grin]

[attachimg=5]

 

[ear3]

Nice test [member=44099]Cheese[/member] !  I am going to work in the washers next time I use the clamping elements.

I agree with the others that something that will be CNC'd needs to incorporate a more robust fastening method than some simple side clamps. That's truly a recipe for disaster.  [scared]

However I was surprised that no-one seemed to be interested in suggesting solutions for this clamping issue when they weren't using a CNC. Surely there must be someone out there that has and HATES this issue and just wants to clamp parts to the bench without the edges of the part lifting.

So I decided to try a very simple test.
Photo 1...clamps placed on a MFT, the clamped material is held down by hand and the clamps are tightened.
There is .025"-.030" of space under the material.

[attachimg=1]

Photo 2...clamps placed on a MFT, the clamped material is held down by hand and the clamps are tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is .012"-.015" of space under the material.

[attachimg=2]

Photo 3...clamps placed on a MFT, the clamped material is held down by hand and a fender washer is added to the clamps and they are  tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is .002"-.003" of space under the material.

[attachimg=3]

Photo 4...clamps placed on a MFT, the clamped material is held down by hand and two fender washers are added to the clamps and they are  tightened while the Festool threaded anchors are threaded into the clamps from underneath.
There is less than .0015" of space under the material.

[attachimg=4]

And this is the side view. If you don't want to deal with the feeler gages, check it out yourself, just clamp an item down to the MFT, observe the .030" space under it and then place 2 fender washers on the Festool knob, tighten the knob and the observe the gap...next to nill.  [big grin]

[attachimg=5]

 

[jeffinsgf]

Cheese,

As I understand your test, you were tightening the clamping elements, then putting the knobs underneath and pulling the clamped material down. This makes sense.

Did you try securing the clamping elements with the knobs and fender washers first, then clamping the material?

Just wondering if the result is coming from pulling the clamped material down or from more secure mounting of the clamping element. For repetitive work, it would be nice if the answer was #2.

 

[fignewton]

I’ve noticed this same problem too.  Your test infers that the shaft of the CE is moving inside the bore of the hole, causing the plane of the face to rotate off vertical from the table.  This is what is causing the CE to lift the workpiece.  I’m going to try this.  I recently did a domino glue up of some strangely shaped trim pieces I made and used the CEs to push the pieces together.  I had to pull out my Seneca clamp dogs and toggle clamps to push the pieces back down on the table.  Very frustrating.

 

[Cheese]

Cheese,

As I understand your test, you were tightening the clamping elements, then putting the knobs underneath and pulling the clamped material down. This makes sense.

Did you try securing the clamping elements with the knobs and fender washers first, then clamping the material?

Just wondering if the result is coming from pulling the clamped material down or from more secure mounting of the clamping element. For repetitive work, it would be nice if the answer was #2.

[member=7266]jeffinsgf[/member] I tried it both ways. The first go-around was securing the CE clamps to the table with the knobs & fender washers and then clamping the wood...that worked fine.

For the second go-around I just clamped the piece of wood to the table with the CE clamps and then added the knobs & the fender washers...that also worked well. I wanted to see if when the CE clamp was tightened if there was enough force from the knobs underneath to pull the wood flush with the table top.

The second method I'd think would lead to a more secure form of clamping because as you're puling the wood back to the surface of the table (about 1/32") the wood is also moving a small amount laterally and putting additional compression forces on the CE clamp.

If I had a force meter spring scale, I'd have added an eye bolt to the top of the piece of wood and taken some measurements for both methods of clamping.

 

[edwarmr]

Cheese,

As I understand your test, you were tightening the clamping elements, then putting the knobs underneath and pulling the clamped material down. This makes sense.

Did you try securing the clamping elements with the knobs and fender washers first, then clamping the material?

Just wondering if the result is coming from pulling the clamped material down or from more secure mounting of the clamping element. For repetitive work, it would be nice if the answer was #2.

[member=7266]jeffinsgf[/member] I tried it both ways. The first go-around was securing the CE clamps to the table with the knobs & fender washers and then clamping the wood...that worked fine.

For the second go-around I just clamped the piece of wood to the table with the CE clamps and then added the knobs & the fender washers...that also worked well. I wanted to see if when the CE clamp was tightened if there was enough force from the knobs underneath to pull the wood flush with the table top.

The second method I'd think would lead to a more secure form of clamping because as you're puling the wood back to the surface of the table (about 1/32") the wood is also moving a small amount laterally and putting additional compression forces on the CE clamp.

If I had a force meter spring scale, I'd have added an eye bolt to the top of the piece of wood and taken some measurements for both methods of clamping.

Where are the washers being applied? To the knob under the MFT?

 

[Cheese]

Where are the washers being applied? To the knob under the MFT?

Yup...just providing a larger and more substantial bearing surface for the knobs.  [smile]

 

[thender]

Just put a shim under the back end of the clamping element slider;  this will directly counteract the lifting at the workpiece.

But...  I agree that clamping elements are a very bad choice for CNC work.

 

[Stone Message]

If you have to use these Festool clamps for CNC work then you should have two on adjacent faces of a rectangular or square piece of work and these should be pushing against a fixed stop. The clamps can rotate around the centre of the peg hole and so, in my humble opinion, are totally unsuited to this kind of work.

I use these clamps a lot and would not part with them for all the tea in China but would never use them for CNC work holding.

Peter

 

[edwarmr]

Where are the washers being applied? To the knob under the MFT?

Yup...just providing a larger and more substantial bearing surface for the knobs.  [smile]

Thanks Cheese! I wonder why Festool doesn't just change the knob and incorporate a built in washer? It would be simple enough for them.

 

[bertv]

Anything with spring in it won’t hold up when vibration is an issue. There are better ways to clamp down for cnc. Eg check out Marius Hornberger on YT — He has some fresh ideas.

 

[Cheese]

Thanks Cheese! I wonder why Festool doesn't just change the knob and incorporate a built in washer? It would be simple enough for them.

I think that like a lot of Festool products this item has been the subject of after-market scope creep. It was designed and marketed to solve a particular problem and because it excelled at doing that, at some time others wanted to extend its capabilities into areas where it was never designed to operate. It was designed as a simple clamp to hold down parts that needed to be hand sanded or machine sanded. Now we're talking about it being used as a hold down for CNC machining.  [eek]

This is very similar to the Systainer situation where it was designed to contain and to hold, but not designed for shipping purposes.

However, to your point, it would be relatively easy to incorporate a thick washer integral with the Festool tightening knobs to alleviate/minimize this condition. I looked at the McMaster-Carr book this afternoon and there were some interesting washer options.

The fender washers I used were .060" thick so if you use two of them they would be 1/8" thick...that's approximately what I was looking for today.

After my experiment, I just threw a half dozen fender washers into the Systainer that holds the Clamping Element clamps for future use.  [smile]