SMT fence stability

[dirtmover]

My SMT fence has become quite unstable over the years. It rocks and moves at the slightest opportunity. I start a cut and by the time I complete it the fence is at a slightly different angle resulting in a few thou of material being taken off the leading edge of the stock by the trailing edge of the blade. To be clear this is not an SMT alignment problem, the fence is moving regardless how tight I clamp it and how careful I am feeding the stock. I don't see any obvious damage to the fence, the clamp or the pivot dowel.

I'm sure this has been answered but I cannot find it. Is this a known issue? Is there a fix?

I'm beginning to think that there is fundamental design flaw in the way the fence is secured.

[LCHIEN]

It is pretty secure in my experience. The BT3 FAQ has some section devoted to this issue.

First you have to have the black pivot in the base secured to the hole provided on one side or the other of the SMT or it will move!
Then you have to have the right set of hardware securing the miter fence and miter holder to the SMT - nothing between the fence and the table. and only a 5/16-18 hex head bolt in the slot... a number of issues I recall people putting flat washers under the bolt head and under the fence and missing the black pivot or having the black pivot in the slot and not the right or left side holes.

The Knob on the miter holder has to be tightened fairly securely, especially if you are using the accessory miter clamp option.

But being over an inch wide, there's no way it should rock forwards and backwards unless you don't have it flat on the table, like the extra washer I described. The bottom of the miter fence should be absolutely flush with the table.

[Jim Frye]

My 1993 SMT fence is still rock solid and it's been on/off thousands of times. Is the issue perhaps rooted in the SMT itself? Are the four clamps that hold it to the saw rails locking tight? Are those clamp mounts secure where they bolt to the SMT body?

[dbhost]

You don't have to gorilla clamp the thing down, but you DO need to snug the lock knob down such that you don't get movement, likewise you absolutely MUST have the black in in the receiving hole on the SMT.

I've never had the miter fence move when I have it secured properly, but miss an important step and it will move on you...

[LCHIEN]

My suggestion: Post some pictures here for critical viewer analysis. Several angles and reasonably close up.

Like these

Most important is getting the bolt and the black post into the proper holes as shown by the arrows. And nothing between the miter holder (black block) and the bolt and table.


And screwed down absolutely flush to the table



And don't cut the tips of your fence off.

[leehljp]

In addition to the photos of Loring's above concerning the hole for the black tab, there are other picts of his showing another part that is very helpful also. Look on the left side of the SMT and you will see a small black flip up - flip down lever. If it has not been used it may be stiff. Flip it up and pull the SMT fence back against it (and with the right side of the fence, specifically the black tab on the bottom in the hole on the right side) this right side tab becomes the pivot hole, the center handle/bolt becomes the lockdown, PULL the SMT fence back to the flipped up black metal tab on the left side.

This gives a 3 position lock for the fence, which should be sufficient (unless cross cutting a 6ft to 8 ft board.). The small lever on the left side of the SMT is adjustable with a flat screwdriver. For the correct position, get a known good 90° square and square the SMT fence to the blade. Adjust the small black lever to the fence. At this point, you can fold the lever down when not using the fence in a 90° position, and then flip the black lever up when you need another 90° cut.

Using Loring's picts, notice the black flip up lever on the left side.

[d_meister]

My SMT fence has become quite unstable over the years. It rocks and moves at the slightest opportunity. I start a cut and by the time I complete it the fence is at a slightly different angle resulting in a few thou of material being taken off the leading edge of the stock by the trailing edge of the blade. To be clear this is not an SMT alignment problem, the fence is moving regardless how tight I clamp it and how careful I am feeding the stock. I don't see any obvious damage to the fence, the clamp or the pivot dowel.

I'm sure this has been answered but I cannot find it. Is this a known issue? Is there a fix?

I'm beginning to think that there is fundamental design flaw in the way the fence is secured.

By your description, it had been fine for a long time. I would suggest placing a straight edge across the SMT at the location of the fence. My guess is that there may be some crown that has developed over the years to the extent that there is little friction helping hold the fence. Mine actually behaves similarly, but I haven't followed up. Thanks for the nudge!

[dirtmover]

LCHIEN the pivot is secured in the hole in the right hand side of the table. The pin fit is snug but there is some discernible movement across the width of the slot, I measured this as 0.008" back and forth movement at the fence face adjacent to the pivot. The hardware is what came with the saw, bolt, clamp and washer between the knob and the clamp. I've not put anything extra in there.
I've checked the fence and table for flatness with a straight edge. By rocking I mean it's relatively easy to tilt the fence backwards a touch towards the user thus raising the front face of the fence off the table.
The bolt head is properly seated in the slot with flats running against the edges of the slot.

Jim Frye the table is perfectly aligned, runs smoothly and there is no notable play. The movement is seen in the fence and observed by looking at the miter indicator. I set it to zero and after a few cuts it is off by half a degree or so.

dbhost I've tried various amounts of tightening up to what I'd normally regard as over tightening considering the parts only are plastic.

@leehljp Yes, I do use the zero stop but the fence tends to move away from it rather than towards it.

d_meister I've had the saw for 21 years and this issue has started relatively recently. I've been living with it but my current projects require a bit more precision. As mentioned above I've checked the table and fence bottom for flatness.

I realise the design intent of this clamp is to secure the fence by leaning forward into it. I do, however, observe that when the knob is tightened there is a gap between the clamp and the leading face of the fence. Now, maybe I'm wrong here but I suspect the intent is to have contact here to hold the front of the fence down.



I have tried adding shims at the locations marked
1 - to fill the gap at the front
or
2 - to tilt the clamp forward more
Either of these result in a significant improvement to how solid it feels.



So is this gap normal? Has my clamp become worn or distorted somehow? I've inspected the plastic closely for any signs of distortion or fracturing.

[Jim Frye]

The front edge of both of my SMT clamps (BT3000 & BT3100) do not touch the top front of the fence. Your nbr. 1 spot. The clamp holds just the rear top part of the fence and the SMT fable top. I never liked hollow plastic castings for tool parts and fill them with number 7.5 lead shot and epoxy. This adds strength, stiffness, and mass to the part and they work much better. I suspect the bottom of your clamp might not be square to the top and is not pulling straight down when tightened.

[Jim Frye]

One more idea. Are the slides on the clamp interfering with the clamping process. My SMT is covered with a project and I can't mount the fence on the SMT to look any closer.

[Black walnut]

Check the orientation of the black pivot point. It has spring tabs on one side, turn it 180° and see if that fixes the issue.

[dirtmover]

The front edge of both of my SMT clamps (BT3000 & BT3100) do not touch the top front of the fence. Your nbr. 1 spot. The clamp holds just the rear top part of the fence and the SMT fable top. I never liked hollow plastic castings for tool parts...

Well that's an eye opener. I wonder why anyone would design a clamp that extends over the entire fence but only makes contact with the back part of it . I'm with you on the plastic parts. I've always felt there is way too much plastic on this saw.

The clamping face plane is parallel to the base but it is slightly shorter than the fence height so it will have a natural tendency to want to tilt the fence back when tightened.

Not sure what to say about the ears that ride in the slot. I don't believe they interfere in any way.

Check the orientation of the black pivot point. It has spring tabs on one side, turn it 180° and see if that fixes the issue.

I've tried both directions and it doesn't make a difference. Not sure if there's a correct way but common sense would put the solid part on the blade side. This part slides very freely in my fence so it has given up much of its springiness.

[GrumpyDad]

eBay seller has a very nice CNC replacement for the plastic part

[LCHIEN]

Those metal replacements on eBay look great.

https://www.ebay.com/itm/293567129301

Or else make your own... ala Rod Kirby

[dirtmover]

Yeah, I saw that a while ago, it looks impressive but $73 shipped is a bit more than I'm prepared to invest in this problem. I think I'll print a second pivot for the left hand side which will at least solve the problem when making 90° cross cuts.

[LCHIEN]

3-d printed Pivot on eBay for $4.50 seen recently.
But two pivots might be hard to align at exactly 90 to the bade.

Miter clamp metal only $42+6 shipping.

https://www.ebay.com/itm/293567129301?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Dc00e03a5685d415aba1d8cc1ec24e5e7%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D354015266169%26itm%3D293567129301%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DRyobi&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Abfca1eb7-c35a-11ec-9bd8-06c97895c3f2%7Cparentrq%3A58b214791800a768fe31082bfffee046%7Ciid%3A1

You can make one as I showed for next to nothing.

[capncarl]

If the EBay seller of metal BT3 parts would make ALL of the plastic BT3 parts in metal! A lot of problems with the saw would go away.

[LCHIEN]

You can get the miter clamp, and the rip fence roller guide in metal - I think those are the parts that break frequently with long age and hard usage. I've seen metal handwheels but not recently.

[dbhost]

I am presently between contracts, but starting a new one shortly, once I get a couple other issues taken care of, I am ordering one of these things. I fully agree, get rid of many of the plastic bits and bobs and most of the problems with this saw go away. I doubt metal SMT slides would be a good idea though...