problems with grinding sleds

[fujimo]

Any of you folk having problems with wooden sleds as soon as you glue on some sandpaper for better traction.

i have some bamboo sleds i got from Kenny years ago- that have really served me well, until i glued on some sandpaper- 120gr sanding belts.
now when the temp changes the sandpaper contracts and expands so much so that it bends the ends of the slep up as much as an inch either end, and cups them as well.
i know the problem was not the sleds.

what do you folk do to improve traction on the sleds.

been thinking about building steel or ali sleds  1/2" thick.
or maybe a thin epoxy scrim with a sprinkled fine sand - like they do on stairs or boat decks to prevent slipping.

currently resorted to sleds we built 2" thick- edge grain, clear and straight iold growth yellow cedar.
seem to be working.   :D  

i think the sandpaper may bend the ali sleds too.
steel sleds will weigh 20lbs- ali will be less than half that.

[Roy from Pa]

I don't use anything. I clamp the infeed side with my hand and when there is enough on the outfeed side I clamp that end.

[fujimo]

yup i do that too mate,but they can slip at the most inopportune times.!

[fujimo]

maybe when they machine the tapers on, they could machine in a small step at the end_ maybe 60 thou- just to hold the butt end of the lams in place.
 and then grind from the thin end.
thinnest lam one can realistically do on the .001 sled is about 70 thou and .100 on the .002 sled.

anybody had hassles grinding lams from the thin end?

[kennym]

I just make the sleds with 50 grit paper and no probs with the lam slipping. One thing to look at tho, a couple times my pressure rollers got sawdust in them and weren't doing their job, so cleaned them and back to normal...

Grinding from thick end I can do .045 on a .001 and .080 on a .002 taper that are 36" long. I'm sure the sander would eat it if it was from the thn end that direction. But I guess I grind wedges and power lams thin end in first, but you have to stalk the last .015 or so...

[fujimo]

thats what i thought about grinding from the thin end Kenny.
yea- there was no problem with the sleds- they worked well for years- when they were just the boo, but with helping new folk building bows etc- i decided to put the paper on, to limit mistakes.
 and in my unheated shop- the paper contracts when it gets cool- and just pulls the sleds into a huge bow    :D  
 and it also pulls them from the sides- and cups the sled too.

[Buemaker]

I have varnished my wood sleds with a thin solvent based varnish before gluing the sandpaper on. Never had problem with them bending.

[Bowjunkie]

Mine is aluminum and I use 3M no-slip stair treads. No issues.

[fujimo]

thanks for the input guys, are any of your sleds stored in a cooler environment?

i like the idea of the 3m stair treads- think i might try them.
the issue is not the humidity- its the temp, as i bring the sleds into the warm house- they straighten out- take them to the shop- within 10 - 15 minutes all bowed up    :mad:  

i think i might get a left over piece of the sandpaper belt, and measure it- then bring it in, and measure it again.

my plan is to go to an ali or steel sled- and i will try that stair tread- and see what happens

thanks for the help and input fella's  

[Crittergetter]

What about glueing paper to the opposite side as well? Might correct the issue ?

[Roy from Pa]

Ah come on critter:)

[Bert Frelink]

Wayne,
I think your problem might be the moisture where you are at,not so much the temp change, just my 2 cents.
I use an aluminium sled with a couple of 2" wide hard Maple tapers glued on with 2 sided carpet tape , but also grind from thick to thin and use 36 grit paper on my sander.        
Cheers.
Bert

[fujimo]

i have been thinking about that Randy    :D
may have to try it
thanks

[fujimo]

i hear ya Bert, but you think the humidity will shrink and expand the sandpaper that much- prior to the sandpaper- the sleds were flawless over the last 3 years- all temps and humidities.
going to have to explore it some more.

 i like the idea of that sled though Bert.
very cost effective way of doing it.
need to get some 1/2" x 4" ali flat bar.

[Bowjunkie]

I think it's more likely that prior to the sandpaper, the higher relative humidity made the wood grow in all directions evenly, and stayed flat enough you didn't notice it. But with the sandpaper on the face of it, the wood can't grow on that surface in length or width so it bows up and cups... i.e. the wood is swelling 'around' the sandpaper.

[Krasus]

Sounds like a humidity issue Wayne.  I took the sleds you sent me and made my own using a-1 Apple ply (3/4"). It is crazy demensionaly stable. My shops not really heated either and I put 80g sandpaper on mine too but I have zero movement. I couldn't find any company that could or would mill steel or aluminum.  Good luck

[fujimo]

very good point Bow Junkie_ makes sense- when one looks at it like that. but you think the moisture can penetrate to sled that fast?

where did you get the apple ply from Cody- that looks like the ticket.
 i have a machine shop here in prince rupert than can do the machined sleds

[Bowjunkie]

How fast did it happen, Wayne? I missed that part. If it happened fast, it might have been heat, but I suspect wood moves more with changes in moisture than it does heat. Is it sealed with something?

[Crooked Stic]

I grind the thin end first thru.On an .002 I go no less than .100. I glue a small strip on the sled as a stop on the thick part end. On thin parallels such as veneers go slow and use finger pressure.
I had an alum. sled for .002s I think it got too hot and developed a bow. another good sled material is corian. Get drop offs at a countertop place and grind it to your needed taper.

[fujimo]

great idea crooked!!

it would bow the sled  in about 10 to 15 minutes- i didnt think it was the wood moving with the humidity- i thought it was the sandpaper moving with the temperature changes