Cutting sled runners - precision issue - Woodworking Talk - Woodworkers Forum
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post #1 of 8 Old 07-23-2018, 11:45 AM Thread Starter
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Cutting sled runners - precision issue

I'm trying to make Willing Ng's crosscut sled, and I'm having trouble cutting the runners to the exact width. He describes two techniques in this video (linked below) starting at 7:24. But the goal is to get a runner within 0.001" of the exact width of the miter slot.

I can't get either technique to work for me, because it seems my fence just isn't up to the precision required. I have the stock fence on a SawStop contractor saw.

Whenever I tighten or loosen the fence, it jumps by about 5 thousands one direction or the other. It's not a problem for most woodworking but it's sure a pain when I'm trying to make an exact cut sled runner within 0.001" for William's technique!

After two hours of test cuts in MDF, the closest I've gotten is 0.002" too large, or 0.004" too narrow. The former doesn't fit, and the latter has a detectible wobble.

Anyone have any cool tricks up their sleeve for getting this cut exact?

Thanks!


https://youtu.be/UbG-n--LFgQ?t=1044
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post #2 of 8 Old 07-23-2018, 12:23 PM
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Take the .002 too large and run a sanding block with 220 paper up and down it a few times.
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Alexis de Tocqueville was a very smart man.
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post #3 of 8 Old 07-23-2018, 12:33 PM
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even tight wood runners will loosen over time. I undersize mine slightly, and place 4 small brass flat head screws on one side, maybe #4, where they will contact the machined edge of the miter slot. then you can adjust them to take the slop out.
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post #4 of 8 Old 07-23-2018, 02:01 PM
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Trying to cut anything to within a thousandth on a table saw is absurd. If you must use wood or MDF then make it oversize and trim with a block plane or sanding block. I dunno what the stability of MDF is with humidity, but wood will certainly change by more than a thousandth from day to day.

For table saw runners I use 3/4 X 3/8 steel bar stock.

Dave in CT, USA
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post #5 of 8 Old 07-23-2018, 04:10 PM
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"After two hours of test cuts in MDF, the closest I've gotten is 0.002" too large, or 0.004" too narrow. The former doesn't fit, and the latter has a detectible wobble."


Either of those dimensions is perfectly acceptable. If it is the 0.002 to large then simply lightly sand. 0.004 is a fine fit.


When I made my sled runners I never measured either the miter slot nor the runner that I cut. I just cut the oak very slightly large and sanded then it fit.


This is woodworking, not machining the cam bearings for your Ferrari.


George
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post #6 of 8 Old 07-23-2018, 09:44 PM Thread Starter
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Possibly worth commenting that I'm making the runners out of nylon from a cutting board for stability, not out of wood. I'm not sure how it will sand, I'll have to try that.
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post #7 of 8 Old 07-23-2018, 10:17 PM
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Quote:
Originally Posted by IdahoEv View Post
I'm trying to make Willing Ng's crosscut sled, and I'm having trouble cutting the runners to the exact width. He describes two techniques in this video (linked below) starting at 7:24. But the goal is to get a runner within 0.001" of the exact width of the miter slot.

I can't get either technique to work for me, because it seems my fence just isn't up to the precision required. I have the stock fence on a SawStop contractor saw.

Whenever I tighten or loosen the fence, it jumps by about 5 thousands one direction or the other. It's not a problem for most woodworking but it's sure a pain when I'm trying to make an exact cut sled runner within 0.001" for William's technique!

After two hours of test cuts in MDF, the closest I've gotten is 0.002" too large, or 0.004" too narrow. The former doesn't fit, and the latter has a detectible wobble.

Anyone have any cool tricks up their sleeve for getting this cut exact?

Thanks!


https://youtu.be/UbG-n--LFgQ?t=1044
You need to call Saw Stop and find out how to set your fence. To pay as much as you did you deserve better.

Don in Murfreesboro, TN.
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post #8 of 8 Old 07-24-2018, 02:38 AM Thread Starter
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Thanks to everyone who commented. I stopped worrying so much about what the calipers said and just took a close cut and sanded it till it felt right. It turns out sanding nylon from a cutting board works ok, though it's a little slow.

Anyway the runners are on the sled and the fit feels super solid. I've got the fences cut and will finish the assembly & squaring tomorrow.
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