The Kreg bench clamp on the MFT (for those who live in a metric world)

[arso_bg]

Hi all

There are no doubts I think that the Kreg bench clamp can be a very useful addition to the Festool MFT in a numerous situations. With this thought in mind, a year ago I bought one clamp to experiment on my MFT table.
Originally I intended to use it on the upper T slot of the table profile. It appeared that this is not very convenient and in addition to that it is quite easy to damage the profile of the table. I tried to fix the clamp trough the holes of the table but the bolt that came with the clamp was too short. I needed a longer 5/16 bolt, but I could not find one. Living in a metric world it appeared to be quite a difficult task for me.

What I did recently is that I took an M8 bolt which is very close to 5/16 and decided to try how far I can go with it. I put some oil on the bolt and using a wrench forced it a few turns forward, than back and again a few turns forward. In a minute I got it about 15 mm deep into the clamp. The threads of the bolt were smashed but it holds very firmly. Having a bunch of Festool knobs I replaced the original bolt, which is also M8 but shorter and I have got the perfect knob for my Kreg bench clamp. Now I can fix it on every hole of the MFT table within seconds.

 

[JeromeM]

Hi all

What I did recently is that I took an M8 bolt which is very close to 5/16 and decided to try how far I can go with it. I put some oil on the bolt and using a wrench forced it a few turns forward, than back and again a few turns forward. In a minute I got it about 15 mm deep into the clamp. The threads of the bolt were smashed but it holds very firmly.

Wouldn't an 8mm tap have worked better?

 

[arso_bg]

Wouldn't an 8mm tap have worked better?

Well this is one possible solution of the problem that I also considered, but since I am not quite sure what will be the result of such an exercise and being afraid to damage the clamp this is the solution that I found for the time being.

 

[AlexThePalex]

Wouldn't an 8mm tap have worked better?

Well this is one possible solution of the problem that I also considered, but since I am not quite sure what will be the result of such an exercise and being afraid to damage the clamp this is the solution that I found for the time being.

The method you used was a lot more damaging than tapping an M8 thread would be. If you're not experienced with tapping it may look like a hard thing to do but it isn't. It is really very simple. It will leave a nice clean cut and an M8 thread that is a lot easier to use then cramming a damaged M8 bolt into a damaged 5/16th thread.

 

[johnnyinnb]

For those of you on this side of the pond this knob from lee valley,  http://www.leevalley.com/en/hardware/page.aspx?cat=3,43576,61995,61629&p=61629 with a 5/16Th bolt is a perfect fit, minutes after reading this thread i got a package from them with the knobs and t bolts to make jigs for the mft and walko benches, I just happened to have an extra clamp on hand. the knob has a 3/4 " shaft that fits in the 20 mm holes in the benches, thanks for the idea.

 

[arso_bg]

Wouldn't an 8mm tap have worked better?

Well this is one possible solution of the problem that I also considered, but since I am not quite sure what will be the result of such an exercise and being afraid to damage the clamp this is the solution that I found for the time being.

The method you used was a lot more damaging than tapping an M8 thread would be. If you're not experienced with tapping it may look like a hard thing to do but it isn't. It is really very simple. It will leave a nice clean cut and an M8 thread that is a lot easier to use then cramming a damaged M8 bolt into a damaged 5/16th thread.

Thank you Alex for your remark!

I have to admit that I am not very skilled with tapping threads and that I do not know well the standards for the different kinds of threads. This is one additional reason for my post.

I understand very well that it would be much better to have a clean M8 thread on the Kreg clamp when used with an M8 bolt. The reason for my concern is that I will be tapping the new M8 threads over the existing 5/16 threads and not in a clean hole. So the result will be not a clean M8 tread as you say but something different - or am I wrong?

Can someone more experienced help here?

 

[JeromeM]

Thank you Alex for your remark!

I have to admit that I am not very skilled with tapping threads

Very few skills are needed when tapping threads. the main one is to keep the tap at 90 degrees to the work

and that I do not know well the standards for the different kinds of threads.

Very few people either need to or do know  the standards for the different kinds of threads

Just use the correct size tap ore die

This is one additional reason for my post.

I understand very well that it would be much better to have a clean M8 thread on the Kreg clamp when used with an M8 bolt. The reason for my concern is that I will be tapping the new M8 threads over the existing 5/16 threads and not in a clean hole. So the result will be not a clean M8 tread as you say but something different - or am I wrong?

Can someone more experienced help here?

If the depth of the 5/16 threads is less than the minimum depth of an 8mm you will have a clean thread.

if it is a bit more than the minimum depth of an 8mm, then the if you use an 8mm tap then you will at least be able to use any 8mm thread without damage.

as it stands now you have something that is neither an 5/16 thread nor an 8mm one.

It may be that this is OK

Only time will tell

 

[arso_bg]

Thank you JeromeM!

If I have to be honest I don't care at all what kind of a thread I have until the bolt holds firmly the clamp. And this one holds it firmly.

But I am anyway curious whether I could improve the situation. 5/16 equals to 7.9375 mm which is a bit less than 8 mm. Does it means that the maximum depth of a 5/16 thread is 7.9375 mm because I actually can measure only the bolt an its external size seems to be a bit less than 7.9 mm. (Unfortunately I do not have a digital caliper and I am not able to read exactly the size of the bolt)

 

[tbellemare]

Although the major diameters are similar, if the pitch is different enough, you should (theoretically) be able to tap the hole again and screw in the 8mm screw. You will essentially have intersecting helices. It won't be as strong as a native 8mm hole but it may not matter.

Tom

 

[AlexThePalex]

And you could always go to M10 instead of M8.

 

[Michael Kellough]

And you could always go to M10 instead of M8.

Going to M10 would require drilling a larger hole in the clamp base.

Slowly run the M8 tap into the threads already swage formed by the M8 bolt.
The tap will cut away the swarf that merely causes friction and will make the M8 bolt easy to use.
Since the two threads are close to the same diameter there the remaining cross threaded helix
should be plenty strong enough for the pressure the clamp needs to apply.

You can use the tap in a cordless drill at low speed or simply hold the square end with an adjustable wrench.
Just make sure it's run into the existing thread nicely before applying torque.

 

[AlexThePalex]

And you could always go to M10 instead of M8.

Going to M10 would require drilling a larger hole in the clamp base.

For an M10 tap you need to pre-drill with 8,5 millimeter. This is just half a mm wider than the 7,935 mm the hole already is. You can tap it right away without pre-drilling and forget about the 0,565 mm. Oh, and drilling a hole isn't even that difficult I think.

 

[Michael Kellough]

The drill for 5/16-18 tap is letter "F", equivalent to 6.6 mm so it'll be a little harder than you think to run an M10 tap into the existing hole. Go slow and careful and it'll work. You are right about drilling it out. It should go really fast.