Tail Vise binds during travel

[storri]

Situation: I have built the front top section out of 5" T x 1.75" H Hard white maple. The front section has been planed down to approximately 4.75 inches.

Problem: When I install the tail vise rails with their shims so that I get the top of the rails at 4.5 inches (1/4 inch below the top) along with the dog plate and the tail vise screw I see that the plate binds during its travel. If I fully extend the dog plate away from the tail vise end (mark it as 0%) and use the tail vise end as 100% then:

 

• 0% - < 50%   - Easy movement
• 50% - 65%   - Noticibly harder
• 70% - locks hard

I still have about 2 inches of travel left. I thought the dog plate should stop when it hits the tail vise flange screws.

 

Installation:

 

Here are my steps that I did during installation:

 

1. Install rails and dog plate. Ran movement. Ok but after further investigation I noticed that the left rail was about 1/4 inch lower than the right. So I added a 1/4 inch shim under the left rail.
2. Install rail and dog plate with shims. Ran movement. It was okay.
3. Installed four screws. Ran movement. It was okay. Checking the right rail I noticed that it was about 3/8 inch below the top. So I added an 1/8 inch to the right. Checking both sides I noticed that each was about 1/4 inch below top (given 3 3/4 inch approx rail grove and a 3/4 inch rail the top of each rail should be about 1/4 below the top surface)
4. Ok so turning off my OCD nature I installed the tail vise screw. That is why I noticed it bound about 70% into its travel.

Attached are two scans of my measurements. The first one (tail_vise-1a.jpg) are the width measurements. The second image (tail_vise-2a.jpg) are the depth measurements. Each drawing was made as if the viewer was standing at the tail vise screw.

 

 

[thewoodwhisperer]

Hey Stephen. It feels like I walked into the middle of someone trying to solve a complex calculous problem. What would really help here is a few pictures of the installation itself, giving us images of the loosest position and the tightest position. Also photos of the rails and your shims would be good.

[storri]

I was saving Calculus for later. I figured you provide more details first.

 

What perspective do you want of each of them? Top Down? I will see what I can convince my smartphone to do.

[thewoodwhisperer]

Top down and bottom up. Also, a close up where you think the binding is occurring. We need to determine if the the binding is in the wood or in the hardware, first of all. Basically, just trying to substitute as best we can for not being there myself to take a look at it. These things can be tricky for that very reason.

[Eric.]

My first instinct was to ask for pictures, too, but then I thought maybe they wouldn't help anyway since even an error so minor it couldn't be seen in pics could still cause the binding.  It's a simple mechanism but it has to be installed with a fair amount of precision.  But because it's a a simple mechanism, there are only so many possible causes of the problem:

 

- The rails have to be parallel and perfectly coplanar with each other.  Are they?  I had a little trouble following your description above (not you, just the complexity of the issue), but you mentioned discovering discrepancies in measurements of 1/4" and 3/8"...those are pretty huge discrepancies...how did that happen?

 

- Did you put a straight edge on your rails before you installed them?  Mine were straight, but at least one of Marc's had a little bow or twist to it.  You should be able to straighten them back out when you screw them in, but you should be mindful of their straightness before and during the install so you can address that issue if there is one.

 

- The nut block needs some wiggle room between the two rails...if memory serves, I think BC recommended at least 1/16".  Does it have that wiggle room?  I'd give it even a little more room than that.

 

- One last thing...because the nut block is binding as you move it toward the end cap, but it moves freely farther away from the end cap, I'll also introduce the possibility that your vise screw hole is not accurately located.  The farther away the nut block is from the end cap, the more forgiving any inaccuracy in the vise screw installation will be. But as you draw the nut block nearer the end cap, the greater the degree of inaccuracy becomes, and the more likely to bind up.  Is your vise screw hole accurately located?  Did you take all your measurements from the top and front of the slab?  The vise screw should be parallel and coplanar with the rails.  Is it?

[storri]

Q: Are the rails in coplanar and parallel with each other?

 

A: Yes. I checked the corner-to-corner measurements to see if the two rails are in parallel. I also checked to see if they were perpendicular to the end cap.

 

 

Q: Did you put a straight edge to your rails before you installed them?

 

A: Yes they are. I could not notice any apparent defect.

 

Q: Is there wiggle room?

 

A: Yes when the vise is fully extended but not so much when its retracted. I think I noticed something. While the rails appear to be parallel and square I think there is a bit of uneveness with the side against which the right rail sits. A sign I did not keep the router tight against the guide strip I clamped to the bench. I would say that it is something a quick run of sandpaper or light paring chisel work can't cure.

 

Q: Is your vise screw hole accurately located?

 

A: Yes I believe so. Even though my thickness is difference I used the template in the plans. I printed them to without scaling and double checking the 1 inch marks with a ruler. That was fine. What I think is happening is the area beneath the screw is too thick. The plans called for the thickness between the top and the screw area to be about 1 15/16 inches. If you look at the photos you will see a large gap on the side of the nut block. I shifted it to the right so we could see how much horizontal wiggle room we have. The telling part I think is between the nut block and the 'bottom' of the screw area. There is hardly any room. Using my calculus crib sheet and my hand OCD dail caliper I see that that thickness is greater than 1 15/16 inches. Its almost 2 inches. I think when I was being extra careful of not going too deep I failed to go deep enough. So when the rails are screwed in with their shims the nut has barely enough clearance when fully extended and none up near the screw. This is because the thickness increase ever so slightly from the extended end up to the vise wheel end.

 

Q: Did you take all your measurements form the top and front of the slab?

 

Yes.

 

Q: Is the vise screw in parallel and coplanar with the rails?

 

Yes. When I used the template to mark my holes I ensured that I drilled the holes accurately on a drill press.

[storri]

Update

 

I used a card scraper on its end to clelar up the area below the wood screw. When I got picky on the shims to fix the depth issue for the rails that makes it work when its upside down. When I turned the bench over it operates but when I fully retract it the action seems to resist a bit until I reach about 50% extended. After which it clears up. Retracting it back again gives good motion until it binds again.

 

Q: Is the vise functional?

 

Yes. It is not perfectly functional but all I need it to do is move about 6 inches. If I need to clamp a longer board I will move the bench dogs.

 

Q: Would I like it perfect?

 

Yes but it requires a redo and a CNC machine.

 

Q: Would I recommend this to someone?

 

It is certainly non-trivial to get three pieces of metal to be in the same plane in three dimensions such that the motion is flawless. So would I recommend this to someone. Yes with a condition: "Understand this is a setup is a joining of a metal mechanism to a wooden structure. It is not as perfect as machining it." There is going to be not quite right motion or fit. In the end I want a functional bench. The vise works great in half its range. I am too tired tweaking it to be 100% perfect. So I am just going to move on to the next part since to get it 100% perfect requires a complete redo of the front section of the top.

[Trip]

Can you use machinists marking dye in the rail slots to see exactly how it binds -- top of rail, bottom of rail, inside, twist, etc?