Tight Miter Fence Clamp Allows Fence Movement

[partialresponse]

I find that even if I really tighten the miter fence clamp knob, the miter fence still moves a little (rotates by 1/2 a degree or so) with moderate force applied to the end of the fence closer to the blade. This makes it difficult to get accurate crosscuts because the fence moves enough during the cut to rob me of any accuracy. Initiallly I though the source of the problem was simply insufficient tightening of the fence clamp knob, but that's not it because even when it's as tight as I can manage the fence can still rotate somewhat. Is there a solution for this? Maybe I need to change my technique also?

Thanks
Kofi

[Sawatzky]

Mine had the same problem. My solution was to use a C clamp in addition to the regulrar clamp. I secured the C clamp to the miter fence and the bottom of the sliding table. This extra clamp made it rock solid. It was still a pain though and was one of the reasons I never really liked the SMT.

[pelligrini]

What's moving? I mean where is the movement coming from? How tight a fit is your pivot point (the little plastic insert that goes into the table)? Do you see any movement at the clamp knob mechanism?

I picked up a well used miter fence a while back and there was a little play in the pivot that would cause problems. It wasn't all that tight in the hole, and it moved a little on the fence too.

[JR]

Is it possible the whole table is moving? This can happen if the sliders/adjusters are set up a little sloppy.

JR

[LCHIEN]

this is explained in the FAQ.
The miter clamp has a special design that not only pushes down but also pushes the workpiece toward the miter fence; this compound action is both good and bad. On the Good side, this assures that the workpiece is flush to the miter fence. On the Bad side, under the conditions described below, it can actualy pull the miter fence off 0°.

If the miter fence is not real tight, then overtightening the miter clamp can pull the miter fence off its original angle, as you noted.

I find I can either tighten the miter fence more OR I can tighten the miter clamp less to prevent moving the miter fence. I find I don't want to tighten the miter fence more than I already do so I usually limit how tight I make the miter clamp when I use it, this hasn't seemed to prevent its holding down the workpiece any. One reason I don't overthighten the miter fence knob is that the nut on the bottom can dent or deform the groove in the aluminum underside of the SMT, since aluminum is a somewhat soft metal.



I suppose its a matter of perception as to whats' overtightening or not, but now that you know, you can take some action to limit the forces.

[Black wallnut]

Let's start with the basic questions:

1. Do you have it assembled correctly?
2. Are we talking about the miter clamp (an attachment that holds a work piece)or the Miter Fence Holder and clamp (the part that holds the miter fence to the SMT)
3. how is it moving?
4. Is the piviot installed correctly in the bottom of the fence?
5. Is the piviot installed into the SMT hole closest to the blade?

The answer to all of these questions will help us help you. Most miter fence problems have been traced to incorrect installation or assembly.

[partialresponse]

Let's start with the basic questions:

1. Do you have it assembled correctly?
2. Are we talking about the miter clamp (an attachment that holds a work piece)or the Miter Fence Holder and clamp (the part that holds the miter fence to the SMT)
3. how is it moving?
4. Is the piviot installed correctly in the bottom of the fence?
5. Is the piviot installed into the SMT hole closest to the blade?

The answer to all of these questions will help us help you. Most miter fence problems have been traced to incorrect installation or assembly.

Yes, the fence is properly assembled to the SMT.

I'm talking about the miter fence holder and clamp, not the attachment that holds the workpiece (I don't have one of those).

The movement is manifest as a visible rotation away from the miter fence stop on the SMT when I pull on the end of the fence closer to the saw blade (this will naturally happen during cross cutting if the end of the fence is not supported from behind - the side closer to the operator - by hand.)

Yes, the pivot is correctly installed in the bottom of the fence. And yes, the pivot is installed into the SMT hole closest to the blade.

Thanks
Kofi

[partialresponse]

this is explained in the FAQ.

That discussion pertains to the accessory clamp for holding a work piece to the miter fence (and SMT). I'm having trouble with the miter fence clamp that holds the miter fence to the SMT.

Thanks
Kofi

[pelligrini]

The movement is manifest as a visible rotation away from the miter fence stop on the SMT when I pull on the end of the fence closer to the saw blade

When you put a load on the end of the miter fence try to see where the movement is coming from. You could probably test it with an engineers square. I would align the blade of the square at one of the two possible movement locations (bolt & piviot hole) with the other side on the SMT top. Testing both locations, you should be able to see where it's coming from.

[poolhound]

I am glad this thread started as I have been having a similar problem with mine for some time that I havent been able to figure out what the problem is. the movement is very slight but it is enough to make the cuts out of square. the movement appears to come from the pivot point but I think that is an illusion. I just went out there and while the ridges on the pivot pin do appear slightly worn the fit is still pretty snug. To make sure I just gave it a couple of wraps with some teflon tape and tried again - same problem.

I have a theory - for me at least. I think it is that the clamp is not pulling squarely on the fence. On mine I also seem to have a problem tightening the bolt. Threads are fine, head of the bolt is fine. The clamp head, however, is where I think the issue may lay. I really cant recall what it orginally looked like but is there supposed to be a tab that fits under the front top lip of the slot in the fence rail? on mine there is a discoloration that looks like something may at one time have been attached. Its been dropped a few times so if there was a plastic tab here it could have easily broken.

Check out the photos (click to get a better view) and let me know if there should indeed be something there or is there something else.....

[pelligrini]

I'll take a look at mine when I get home shortly, if someone doesn't take a look at theirs sooner.

You might also check to see if there is any movement in the piviot point where it slides into the miter fence. When I was swapping parts from my miter fence to my long miter fence there was a big difference in a couple of the piviot points. One would move really freely (like sliding off if the caps weren't on) and the other was really tight.

[partialresponse]

Is it possible the whole table is moving? This can happen if the sliders/adjusters are set up a little sloppy.

JR

No, I can clearly see the miter fence pull away from the zero-degree stop tab on the SMT when I apply moderate force to the blade end of the miter fence.

- Kofi

[pelligrini]

Poolhound - neither of my two extrusions have a tab on them both are flat. One is from my 21829 and the other is off a BT.

I was just able to duplicate a similarly described movement from one of the fences. When I looked into a possible cause there was a lot of play in the pivot. It jiggled back and forth some when I turned it over and moved it by hand.

I would think that if you put some force on the fence towards the front of the table when calibrating it, the movement shouldn't be too much of a problem.

[JR]

No, I can clearly see the miter fence pull away from the zero-degree stop tab on the SMT when I apply moderate force to the blade end of the miter fence.

Ok, I getcha now. Truth be told I've never used that thingy.

It's clearly got to be the clamp or the pivot. The clamp can be a little awkward to set up. The head of the bolt needs to be inside a pair of aluminum rails formed on the underside of the table. If it's straddling one or both of the rails it might not be a firm setup.

That's all I got, pal. Good luck.

JR

[aiyou]

I just went out and checked mine, just because, and lo-and-behold, noticed the same thing.

I recently purchased a second BT3100 from CL, and figured I would test it on this second SMT. Same fence, no play!

My guess at this point is that the right pivot hold on the SMT may be a bit outta whack. Now...how to fix.

Since I have the second SMT, will likely align this one to use as my primary