[johnnyhawkins]

Hi all, I hope you can help!

I'm planning a router sled currently to flatten some large slabs, I'm thinking of using 20mm aluminum cross-rails within which the router would be attached. My question is with the amount of deflection that might be produced from these rails, I've done some calculations using round bar deflection calculators available online and I'm getting the results out to be around 25/26mm deflection for a 2m long rail.

However, this calculation is for just one rail, whereas the sled would have two, also a "point-load" probably isn't the right term for a router spread over 4 cars on 2 rails...

Also note that I don't necessarily require an exact answer to the calculation, my question is really, would 2 x 2000mm(length) x 20mm(diameter) aluminum rails, clamped at either end, support a 1/2" router plus a few components without a noticeable amount of deflection? I suspect they would sag a little but it's only a guess.

Your help is greatly appreciated!

[CNCMAN172]

Hi all, I hope you can help!

I'm planning a router sled currently to flatten some large slabs, I'm thinking of using 20mm aluminum cross-rails within which the router would be attached. My question is with the amount of deflection that might be produced from these rails, I've done some calculations using round bar deflection calculators available online and I'm getting the results out to be around 25/26mm deflection for a 2m long rail.

However, this calculation is for just one rail, whereas the sled would have two, also a "point-load" probably isn't the right term for a router spread over 4 cars on 2 rails...

Also note that I don't necessarily require an exact answer to the calculation, my question is really, would 2 x 2000mm(length) x 20mm(diameter) aluminum rails, clamped at either end, support a 1/2" router plus a few components without a noticeable amount of deflection? I suspect they would sag a little but it's only a guess.

Your help is greatly appreciated!

Big Heavy 1/2" routers will make it sag in the middle with 20mm rails. You might want to go to 25mm rods or better yet, standard flat linear rails which can be fully supported underneath the rail the entire length. Flatten slabs is not a critical application as you will work them with sanders after you finish roughing them. So probably not that critical.

[peteeng]

Hi Johnny - Yes a 20mm aluminium section over 2m will sag alot. Go to a metal supplier or the local hardware that sells 2m lengths and just put them across something and push in the middle, the deflection will surprise you. Peter

[johnnyhawkins]

Thanks for the prompt responses guys, appreciated. Think I'll have to visit a metal shop!

[joeavaerage]

Hi,
even with steel you'll get too much deflection.

If you calculated 25mm deflection for a 20mm diameter aluminum section, and that sounds about right, steel is tree times stiffer than aluminum so for the same 20mm steel section
you'd get 25/3= 8.88mm deflection, which is still too much.

Craig