# Noob question but do cross cut sleds go out of square over time?



## paul_allen (10 Dec 2021)

New to the forum, happy to be here. 

I built a sled about 6 months ago and go it to 0.5mm accuracy over 2000mm using the 5 cut method. This morning I noticed it is out by 2mm over the same distance. Is this common?!?

Sled and fence are made of MDF and screwed together, rails are glued. I am very careful when moving and storing it, so I don't think it has been knocked or damaged. Only other thing could be the saw, but I check that regularly and I'm told the saw is pretty robust and doesn't shift around, it's the AT254LTS.

Any insight would be greatly appreciated!


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## Jameshow (10 Dec 2021)

Moisture / temperature variation???


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## paul_allen (10 Dec 2021)

Jameshow said:


> Moisture / temperature variation???



This is a good point, has been very damp in the workshop the last few weeks.


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## Distinterior (10 Dec 2021)

What is the table slot runner made of and did you seal the MDF with anything ...?

Edit. Jameshow is thinking the same as me....


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## paul_allen (10 Dec 2021)

Distinterior said:


> What is the table slot runner made of and did you seal the MDF with anything ...?



The runners are MDF, and the underside is sealed with paste wax. They are double runners though and still glide smooth.


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## Distinterior (10 Dec 2021)

To be fair, I wouldn't have made the runners out of MDF.....I have a small sled I made for segment cutting on my table saw and used pre sealed MDF for the sled and Oak for the runner.

This time of year, bare MDF is going to absorb moisture and likely to throw out the accuracy of your sled....It may be too late now, but I would think you needed to seal the top as well as the bottom of the sled.


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## paul_allen (10 Dec 2021)

Distinterior said:


> To be fair, I wouldn't have made the runners out of MDF.....I have a small sled I made for segment cutting on my table saw and used pre sealed MDF for the sled and Oak for the runner.
> 
> This time of year, bare MDF is going to absorb moisture and likely to throw out the accuracy of your sled....It may be too late now, but I would think you needed to seal the top as well as the bottom of the sled.



Thanks for the info, I had no idea MDF absorbed moisture like that, seams obvious now. On my new sled then I probably shouldn't use MDF for the fence either, just use it for the base?


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## Fitzroy (10 Dec 2021)

Worth also checking if you've bumped your top and the slots are no longer true with the blade.


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## Peri (10 Dec 2021)

Make the runners out of an old plastic type chopping board - they never go out of true


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