Crosscut Sled Slight Rack

[Charlie Gummer]

Good Sunday Morning All,

I'm nearing the completion of my (first) crosscut sled. 1/2" BB ply laminated on both sides with two hardwood runners. I have the rear fence (away from the operator) on and the runners on.

My issue; until the runners are fully engaged in the miter slots (the sled fully covering the table) there is a very slight angular racking of the sled. My concern is that although the racking is very slight now, as the runners wear the slop will become worse.

I'd like to address the issue (if it needs to be addressed) before I make my first cut. Should I reattach the runners?

Thanks!

[Glen Butler]

If I understand your racking issue correctly, it is that one peice is shifting independent of the other? This is what I did to correct the issue. You will see that the rear fence is a peice of 3/4 ply laminated to the sled. This provide more stiffness to keep the two halves from shifting.

http://www.sawmillcreek.org/attachment.php?attachmentid=136938&d=1262417714


What are you using for your runners. I use hickory, for the cost it is very hard. I very slowly sneek up on the fit with my planer. You can always use a bar sander to loosen them up later if they end up too tight. My sled slides with no binding even if I push it from the far right side.

[Charlie Gummer]

Thanks for the response Glen. To clarify; I haven't split the sled yet. The racking happens with the sled as one piece. If the runners aren't fully engaged in the slots I can shift the hole sled very slightly side to side in the slots.

[Glen Butler]

it sounds like your runners are too loose. You should fix the problem now.

[Rich Neighbarger]

I've seen a nice hardwood runner setup with a few cone shaped holes drilled along the bottom length of each. Then a set screw was installed into each cone shaped hole to adjust for any slop developed over time.

[Bill Huber]

I don't like wood rails, I know there are a lot of people that do but I just found they gave me problems. When the humidity was up they were nice and tight when it was dry they were a little loose.

I bought a set of Incra and they are great, I have had them now for over a year and they are always tight and have never been sloppy at all.


http://www.incra.com/product_jfc_miterslider.htm

[Rich Neighbarger]

Oh, I forgot to mention. I saw a sweet setup using ball bearings that run along the miter slot. It looks like it would resolve any problems with slop. He also had the nicest crosscut sled I have ever seen along with some instructions for those without sleds. Search for "Precision Puzzlemaking Primer."

[Norm Koerner]

If you can locate which part of which runner is the "loose" culprit, you can put tiny screws in that sides about every 3-4". Just leave a few thousands of the head of the screw protrude from the runner. You might need to round the sharp edges of flathead screws, but I'd go for round or oval headed screws. Personally, I use the nylon runners.

[Wayne Jolly]

A couple of years ago I went to a metal supply and bought (among other things) a 12' piece of 3/8" x 3/4" aluminum flat bar. Great stuff for runners. At the time it cost me less than $20.

xeddog

[Phil Thien]

This is why making sleds in two halfs and then connecting them makes sense.

When you connect them, you pull them snug so both runners ride the inside edge of the miter slot. No more play.

[Glen Blanchard]

I agree with Bill Huber. I prefer metal runners...actually I like Kreg's more than Incra's.

[Charlie Gummer]

Very interesting responses, thanks! I like the idea of adding screws to the existing runners but I think I'm leaning towards picking up the Incra (or Kreg). One thing I've noticed is that the Incra are only available in a maximum of 24" lengths. I've made the base of my sled the exact width of my JPS10 Jet contractors saw (26"). If I center the runners this will leave an inch on either side. I don't see that being a huge issue, just a slight reduction in cutting capacity. Any thoughts as to whether I should cut the base down to 24" wide to match the runners?

[Nathan Callender]

This is why making sleds in two halfs and then connecting them makes sense.

When you connect them, you pull them snug so both runners ride the inside edge of the miter slot. No more play.

Phil - can you detail a little more the process of building it in two sections and how you them join them? Do you plan for the zero clearance slot or just cut that when the two pieces are together?

[glenn bradley]

it sounds like your runners are too loose. You should fix the problem now.

I'm with the other Glen, fix it now. I have sleds with oak, UHMW and adjustable aluminum runners. All word well and have remained stable. I am in the foothill basin area of SoCal so I have minimal humidity swings.

All that aside, fix the runners. I set my positions by putting double stick tape on the runners, elevating the runners in the miter slots (I start with a really tight fit) by placing thin strips of wood under them. I then referenced the sled-bed against the fence and lowered it onto the runners. Once stuck in place I apply the screws. I used a card scraper to tune the oak and UHMW runners. The Incra aluminum runners use wedges and screws to expand the bar.

[Glen Butler]

I have not seen a metal bar that I like. The best ones I saw had two points one front one back that you could adjust a brass glide that snugged up the track. The problem is that when one of those glides leaves the miter slot, as they usually do on a crosscut sled, then the sled slops. And they don't make metal runners long enough.

[Roger Pozzi]

Very interesting responses, thanks! I like the idea of adding screws to the existing runners but I think I'm leaning towards picking up the Incra (or Kreg). One thing I've noticed is that the Incra are only available in a maximum of 24" lengths. I've made the base of my sled the exact width of my JPS10 Jet contractors saw (26"). If I center the runners this will leave an inch on either side. I don't see that being a huge issue, just a slight reduction in cutting capacity. Any thoughts as to whether I should cut the base down to 24" wide to match the runners?

I would think that aligning the runners with thefront of your sled will give you all the support you need. That way you have full support starting your cuts and, by the time you get to the end, you would still have support from the cut point to the back of your table. That would change slightly depending on the depth of cut but, still seems to be more than enough given that your rear fence will take up some of that space.
Just my opinion, others may have reasons that this will not work.

[glenn bradley]

One thing I've noticed is that the Incra are only available in a maximum of 24" lengths.

This is a problem that someone else mentioned back in the thread. I use the Incra bars on my smallest sled. The adjustment points are always within the miter slots during use. The issue on this type of bar (or the ones with spring loaded balls or screws or anything else that does not provide a consistent line of adjusted face) comes when an adjusted point of contact leave the slot as it probably would on a sled your size. When that occurs the adjustment and the associated fit get lost.

For larger sleds I prefer continuous guides. There is sometimes the challenge that the slots are not as perfect as we wish they were. This means some concession has to be made while fitting the runners to allow them to move through the required range of motion, freely but reliably.

[Phil Thien]

Phil - can you detail a little more the process of building it in two sections and how you them join them? Do you plan for the zero clearance slot or just cut that when the two pieces are together?

Basically, you make a left and right sled, with runners attached. You make them so the bottom extends beyond the blade 1/8" or more. Then you run them through the blade.

Now you pull 'em snug (towards the blade) and attach the fences.