[RickKr]

I had a chance to work with the dado set that I got along with the new table saw. Set up the dado table insert and set the dado stack for 3/4", more precisely 0.755". Ran a couple test cuts to get it where I wanted it. Had put in a 0.010" shim to begin with, but took it out and the dado slot turned out perfect. Have to tap the plastic miter slot bars lightly to seat them. Just need to screw them in place and they will be ready to go.

You'll notice the base is in two pieces. I did it this way so I could get the dado-ed miter bar grooves to fit the plastic bars snugly and not have to fight with positioning the two grooves in the same base board. The blade faces of each panel match along the cut line and I will line these up when I mount the fences and make a zero clearance cut, and I theory, everything should slide freely with minimal play. If it works, I think it is a slick way of doing it.

I had previously made the front and rear fences, by gluing together two pieces of the 1/2" Baltic birch plywood the bases are made from. Then bandsaw the rough shape followed by sanding. I don't have the screws I want for mounting the fences, so will have to do the one-hour drive to Baker City to get to a hardware store that has brass screws. There are two hardware stores in the town I live in, Halfway, OR, but the one that has better stock and selection in fasteners is close indefinitely due to a collapsing roof. The remaining one that is open doesn't stock any brass fasteners.

I have the brass crews I want for the miter bars, but I'm just too tired tonight to do any more.

Rick

 

[Cherryville Chuck]

I don't know about down there Rick but brass screws are getting hard to come by up here. UHMW is bad for creep meaning that it will continue distorting with pressure on it forever, literally. You didn't say what kind of screw but you may need to countersink the holes and use round heads. I tried the same runners on mine but my sled was narrower and I tried extending the runners out past the ends for more control but the UHMW was too flimsy for that so I took them off and went with hard wood ones.

 

[RickKr]

Chuck,

I'm not surprised the UHMW runners were too flimsy extended beyond the base. I think what I'm using is UHMW, but I'm not sure. It is very slick, very white and shiny. I've had it for year and was originally going to make skid pads for moving heavy machine tools.

I'm not sure how you mean it creeps. The screws I have and am planning on using are flathead. Are you saying I should not use them, but use countersunk round head instead? I can certainly do that; I was going to countersink the flatheads. Please elaborate. BTW, I would call creating a recess for the round heads "counterbored" rather than countersink. The latter means tapered to me.

Brass screws are not getting that hard to find down here, as far as I know. They are expensive and the area I live in is fairly depressed economically, so I'm not surprised the one store doesn't stock them.

Rick

 

[Stick486]

Counter bore and use truss head screws...

 

[Cherryville Chuck]

Chuck,

I'm not surprised the UHMW runners were too flimsy extended beyond the base. I think what I'm using is UHMW, but I'm not sure. It is very slick, very white and shiny. I've had it for year and was originally going to make skid pads for moving heavy machine tools.

I'm not sure how you mean it creeps. The screws I have and am planning on using are flathead. Are you saying I should not use them, but use countersunk round head instead? I can certainly do that; I was going to countersink the flatheads. Please elaborate. BTW, I would call creating a recess for the round heads "counterbored" rather than countersink. The latter means tapered to me.

Brass screws are not getting that hard to find down here, as far as I know. They are expensive and the area I live in is fairly depressed economically, so I'm not surprised the one store doesn't stock them.

Rick

The flat head screws may cause the UHMW to swell under the pressure of the tapered shoulder. I read a good paper on it's properties a few years ago but a quick search didn't turn up anything useful. The paper I read before said that if UHMW, which is what you described is most likely, is subjected to constant pressure it will continue to deform. One of it's uses over here is a low friction bearing plate on the 5th wheels of semi trucks. They have to be replaced periodically and when they get removed they aren't just worn, they have also significantly changed dimension, getting flatter and wider. The couple of articles I scanned said that the material is used in bowstrings and as a traditional type archer one of the things we look for in bowstrings is the resistance to creep, or in other words the tendency of the string material to keep stretching over time.

 

[FreeTime]

I can confirm, the creep is not theoretical. I tried flathead screws with this material once and I could never keep the runners operating smoothly

 

[Nickp]

I would not use any screw that has a taper...it will expand the runner. Counterbore and flat bottom (truss, modified truss, pan, etc...). The more the merrier...

 

[RickKr]

Excellent. Thanks for the information. Knowing the "why" really helps. I can easily do flat bottom.

Dang, I've had those brass screws for decades. I was glad to see I had enough, they were the right size and I finally had a use for them. They may go on the list of things to get from Baker City. I definitely can put the flat bottom in, it is just a matter of what type of screw to use.

Will it work to just screw into the plywood? Or should I use threaded inserts in the plywood. I have an ample supply of the inserts, but it means using 1/4"-20 fasteners. I was hoping to avoid through holes for these. No need to give the sawdust a place to collect and get in the way.

Rick

 

[Nickp]

No need for the inserts...just screw the right size screw into the plywood...pre-drilling may help depending on size of screw used...

 

[MYB506]

I used 1/4" round head machine screws counter bored and threaded the UHMW to accept the screws. This was for a large 2 runner sled that I made years ago and it still runs very smooth.

 

[Cherryville Chuck]

Pan head and truss head screws have a lower profile than typical round head type screws. Some screws will hold much better if you drill a pilot hole. Some don't need it as much. In particle board and mdf the pilot hole is close to being a necessity. The screws tear up the fiber so badly trying to get enough bite to keep threading that there isn't much material left to hold them by the time you finish sinking them.

 

[Stick486]

I would not use any screw that has a taper...it will expand the runner. Counterbore and flat bottom (truss, modified truss, pan, etc...). The more the merrier...

excellent...
but you forgot to tell him about the double stick tape, make a clearance hole for screw in the UHMW and that Fostner bits do the best counterbores...
Note:
Truss heads screws, (aka K lath) are large dia heads that also have a very low profile... pilot drill for them and yur golden..

and FWIW..

.

 

[RickKr]

Working Too Late, Too Tired

I was doing pretty well with this sled, until tonight.

I got the runners mounted. Counterbored the runners and used regular round screws because that is all that is available locally. Counterbore that I used is 12mm (0.472") so I will have to check to see if I can find truss/lath screws in Baker City. I wasn't planning on going but things conspire....

I did the runners and rear fence yesterday and earlier today. No problems, other than the sled is a touch snug in one spot. I think I need to open up the clearance hole in the UHMW runners so the screw isn't pushing the runner sideways at all.

I was up very late tonight (last night) with some worries about family matters and could not sleep. So, I figured I'd work on putting in the holes and threaded inserts for the front fence. It was all going well, getting it lined up (square with the saw kerf), pilot holes placed in the bases/fence.

And then I went to counterbore for the screw head relief holes. I forgot to turn the sled over. Counterbores were supposed to go on the bottom. But... I put them on the top.

I'll try plugging these holes/counterbores and then redilling/CBing from the right side. If that doesn't work, I'll just trim off an inch and try again. However, as things happen, I am not sure when I will get back to this.

Rick

 

[Stick486]

No problems, other than the sled is a touch snug in one spot.

shoulder plane is the perfect fix for that...