Convert Stone grinder to Belt grinder

ggardner90 · Post by **ggardner90** » Tue Jan 10, 2012 1:53 pm

i have a stone grinder with a 5.5in stone on it i think that there is a small depression in the stone and the bases are not coming out completely flat, there is a small strip down the center of the ski which does not go away.

there is a "depressor" on the back which looks like it is designed to flatten the stone, i cant seem to get it working but that is a different issue.

so my question is, and i am very new to base grinding and tuning in general, how difficult would it be to make this grinder use a belt instead of a stone. i want to make the switch because all the really nice grinders that i see use a belt. therefore i think that it would be better to use a belt.

any and all ideas would be greatly appreciated

twizzstyle · Post by **twizzstyle** » Tue Jan 10, 2012 2:43 pm

Well they sort of serve two different purposes (as I understand, I'm no expert ski tuner, and I just have a belt grinder). For us home-builders, the belt grinder is for taking off lots of material quickly, and flattening the base. The stone is for final passes and putting the structure into the base prior to waxing.

Converting it to a belt may be a challenge though, depends on your fabricating skills. You could just swap the stone for a drum, and wrap it in sand paper, and you're good to go, but I'd worry that such a short length of belt may gum up and overheat too quick. Ideally you'd have some length of belt (my grinder uses something like 80" long belts), but that would require a second drum for the belt to go around, and then you'll need a way to adjust for belt skew, and it'll all have to fit within the water spraying area, etc...

Anything is possible with a little cutting and welding, but it might not be easy.

ggardner90 · Post by **ggardner90** » Tue Jan 10, 2012 4:40 pm

i was worried about that, so if converting to a belt wont be really easy, i will start trying to get this stone grinder dialed. i have it wired to 120v but the motor is made for 120, or 240 two separate wiring diagrams. on the first couple passes i have to adjust the auto feed because the stone stops spinning half way through the ski. would putting it on 220v solve this or is it just what happens when grinding garage built skis.

how would i check it the ski is what has the convex shape or if it is the stone?

ggardner90 · Post by **ggardner90** » Tue Jan 10, 2012 4:40 pm

i was worried about that, so if converting to a belt wont be really easy, i will start trying to get this stone grinder dialed. i have it wired to 120v but the motor is made for 120, or 240 two separate wiring diagrams. on the first couple passes i have to adjust the auto feed because the stone stops spinning half way through the ski. would putting it on 220v solve this or is it just what happens when grinding garage built skis.

how would i check it the ski is what has the convex shape or if it is the stone?

Dr. Delam · Post by **Dr. Delam** » Tue Jan 10, 2012 6:43 pm

Having a stone grinder without a belt sander really isn't going to help you much. The majority of the work you want to be doing is with the belt sander to get the ski flat first. You can check for flatness with a high quality true bar by holding it up to a light source and seeing where the light is showing through. My guess is that your skis will be showing the light in the center with concave bases.

You don't even really need a stone ground finish and it won't help much if your skis are not flat to begin with.

Hate to say it but you need to belt sand these first before worrying about anything else.

ggardner90 · Post by **ggardner90** » Tue Jan 10, 2012 8:09 pm

theoretically if i had a flat stone couldn't i get flat bases with a lot of passes?

Idris · Post by **Idris** » Tue Jan 10, 2012 11:30 pm

ggardner90 wrote:theoretically if i had a flat stone couldn't i get flat bases with a lot of passes?

Not really, depending on your stone it will be like 300 or 800 grit belt.

I use a 60 grit belt to flatten bases - 100 grit would take 10x longer

MontuckyMadman · Post by **MontuckyMadman** » Wed Jan 11, 2012 11:25 am

IMO a 60 grit belt is way too much and could lead to more concavity.
Depending how the belt is detuned a new belt at that grit could destroy the ski.
Try a couple passes out of the press with a detuned 80 and then move up to 100.
Most of the time, the ski has already had a base edge bevel added prior to hitting a base structuring stone.

twizzstyle · Post by **twizzstyle** » Wed Jan 11, 2012 11:37 am

I do all of my grinding with a 120 grit ceramic belt (but again... don't actually know what I'm doing, just know I get decent results from a new ski out of the press, to a nice gliding surface for the snow). I get my belts made from Econoway Abrasives, it's cheap.

ggardner90 · Post by **ggardner90** » Wed Jan 11, 2012 1:26 pm

do you think it would work if i just put a belt on the stone and had a second drum which i could use to adjust tension

twizzstyle · Post by **twizzstyle** » Wed Jan 11, 2012 4:28 pm

As long as you can flatten the stone first, yes.

But your second drum will probably need skew adjustment, otherwise the belt will just fly off the machine.

ggardner90 · Post by **ggardner90** » Wed Jan 11, 2012 5:07 pm

all i know about scew adjustment is that it is the little dial on the side of my belt grinder. but i dont really know how it works or what it does other than hold the belt straight. how would incorporate that into my design

barnboy · Post by **barnboy** » Wed Jan 11, 2012 6:15 pm

Hey gardner. Twizz, MM, and the rest of the super faithful and helpful folks here (totally serious) have given you some pretty solid intel. While I would not consider myself an expert in the tuning department, I've been getting paid to tune skis for the past 4 seasons now, and have done a WHOLE LOT of skis in that time.

If your stone has a dressing tool on it, you definitely want to dress the stone until you can hear the tool staying in constant contact as it moves across the stone, then you know you're flat.

As for belting first to get to flat, both twizz and MM bring up good points... if your skis are railed, you do want to be careful when belting them, especially with an auto-feed mechanism, as the auto-feed can actually temporarily flatten the railed ski as it's passing over the belt. Once the ski is out from under the pressure of the auto-feed, it original concave shape returns, only now there's material removed from the center of the ski, augmenting your problem.

Now, if you're base-high (personally I find this to be the more desirable condition) then the belt will be your best buddy for getting to flat (or near flat) before dressing the ski with the stone.

The stone can be effectively used as your sole flattening tool, especially if your cranking out base-high skis. If you're finding that your skis are usually railed, you're going to need to re-dress your stone quite a bit as your skis' edges slowly are ground down to meet your bases. As stones are far more expensive then belts, most shops flatten on belts first, to save the life of their stones.

Mini-edgers are the best tool (I know of) to deal with railed skis. They're spendy little units though, someone needs to come up with a good DIY version.

Hope this is helpful...

ggardner90 · Post by **ggardner90** » Wed Jan 11, 2012 7:20 pm

the grinder dose have a depressor but i cannot seem to get it working, i will call one of my engineer buddies now to see if he can help. i guess i will attempt to use the stone for the next couple skis and then once we get some money coming in from sales, try and find a belt, to we can do it the right way.

twizzstyle · Post by **twizzstyle** » Thu Jan 12, 2012 8:56 am

Skew adjustment could be tackled many different ways. You just need a way of very-precisely turning one of the drums (a VERY small amount).

The skew adjustment on my grinder is a little hard to explain. On the non-driving drum, it has an axle that sits in these forks. On one side, there is a wedge between the axle and fork, that has a threaded rod that you turn that moves the wedge up and down. As the wedge moves down, it pushes the axle away from the fork, which tilts the drum. Make sense?

See the axle? Look just left of it, you'll see the brass wedge inside there.

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Convert Stone grinder to Belt grinder

Convert Stone grinder to Belt grinder

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