# 8020 aluminum extrusion for crosscut sled fence



## RobinDobbie (Jan 31, 2013)

I hate to make a long question post, but here goes. A bit of background, then my newbie questions at the bottom. 

I had a lengthy thread not too long ago about crosscut sled problems. One of my enemies was constantly changing temps and humidity levels in the work area(a small shed kit I got from a home center that has no insulation and giant gaps in the seams), and my wood parts would change shape dramatically. I used oak for the runners, and plywood glued up for the fence. The plywood went away first, it was just too unstable. I went to hard maple. The maple honestly might still be fine, I haven't been out in the shop for a while. The oak runners didn't work very long, however. By the time I sanded them enough to get the sled to slide easily no matter the conditions, there was too much play for my taste. I think it's possible the oak was only half the problem. It had been suggested that the cast aluminum on the poorly designed Skil table saw I was using was changing shape with temperatures, as well. I have a new(to me) table saw, now. I got a Ridgid TS3650 with a cast iron top and wings. The standard width miter slots are nice, and they have the T-slot in the bottom. 

To eliminate as many problems as I could, I decided to get Incra miter sliders for the runners. For fence material, one user suggested I use 80/20 aluminum extrusion because it's perfectly flat. I found some on ebay that's 1.5 x 4.5 and 33" long(which was about the length I think I wanted for my sled).

Questions: 

Will the aluminum extrusion be a good choice, or should I just stick with two 1x6 maples glued up? Is there a better metal option?

If extrusion is the way to go, how to attach it to the sled base?

Will the aluminum be changing significantly with temperature changes?

My goal is accuracy beyond what might be necessary. I'm new to this, I get easily confused when things don't line up. I need as little error as possible, and I'm willing to pay for things that minimize that error because the time it takes to figure out where I went wrong just isn't worth it.

I appreciate any and all input!


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## Tman1 (Jan 14, 2013)

The extrusion will be more stable than the maple. The only effect humidity will have on if is maybe some white aluminum oxide on the surface if you allow if to condense there. Thermally, you could see some expansion and contraction if the temperature varies widely enough. I think this would probably only be a few thousandths at most, but it's been awhile since i have looked at aluminum thermal expansion. But, it wouldn't warp and the main issue would be expansion and contraction of the saw kerf.

On that topic, while technically you can use woodworking tools to cut aluminum, I have never been fond of using the same blade to cut wood and aluminum. Because a saw blade optimized for aluminum will be different than the ones optimized for wood and aluminum can be hard on some of the ones optimized for wood. So, if I was going to use aluminum for my sled fence, I would use two pieces with a wide gap for the saw blade and a Baltic birch face. 

You have a couple options for attaching it. You could use t-nuts in the slots with flathead bolts coming up through the bottom. This should be a good way to go, except you have to attach the fence from underneath. You could also drill holes through it and bolt through them. This has the advantage that you might be able to tighten the fence from the top while it is on the saw, making it easier to square up. You could also attach it using aluminum angle, or you could skip the 80-20 and attach the face directly to aluminum angle.


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## plainolebill (Mar 31, 2013)

If you decide to use 80/20 you'll need to use their T Nuts, Nuttin' else will work. :no:


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## RobinDobbie (Jan 31, 2013)

I apologize for not participating in this thread I started, but I figured I'd update. I decided aluminum is just too tricky to attach. The hard maple fence from the sled I made for my Skilsaw is still good, so I think hardwood is the way to go. I needed a jointer and planer for some upcoming projects, anyway, so I just went ahead and got them now to help make sure whatever hardwood I use for fences is flat and square.


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