Building A Swing Arm Belt Sander

[Guitarnut]

After seeing CptRyg's Shopsmith adaptation of the belt sander, I've decided to build one for myself. It wiil be powered by my SS Mark V and have a few design changes from the one he built.

Many thanks to CptRyg for his design and the info he shared with me.

First off, mine will be a direct drive design, sitting perpendicular to the SS instead of parallel which would require a right angle drive. I tried to snag a drive off eBay but they went higher in bid price than I wanted to pay. One less part to buy.

Second change is the belt tension setup. Instead of turnbuckles, I'm using opposing brackets that are anchored a bit better and I think will give me better micro adjustment. I have the mock up modeled with 4 tensioners but I may only need 3...1 on the live end and 2 on the free end. Not sure yet.

The front support panel will be hinged for belt replacement. The plan is to remove tension, unbolt the bottom of the panel and have it swing out to allow the belt to move.

The live end will be clamped to the way tubes of the SS and the free will be supported by a folding leg...this will make storage easier when not being used.

The swing arm assembly will be removable so the sander can be used for other tasks. I will likely add a removable fence for use when the swing arm is detached.





The plan for the tensioners is pretty simple. The bolt head will be fixed in one bracket with a jam nut and the other end will apply pressure against the second bracket using a nut and flat washer and be adjusted with an open end wrench. The belt will provide counter tension.





The rollers will be 3" schedule 40 PVC pipe. It's OD is actually 3.5" inches with ID of 3". I wanted to repurpose an aluminum rolling pin but I can't see spending the money on one when the PVC is plenty strong. The sander's bed will be .25" aluminum plate 6" wide by approx. 32" long.





Mark

[Guitarnut]

I don't have the sanding belt in hand yet but I plan to use a 6" x 80". That sounds like a huge belt but it will actually only net a 31" to 32" work surface.

With 3.5" rollers, I needed to determine the "wrap" distance that the belt would need. Diameter x pi gives me...

3.5 * 3.14 = 11.00. This would be the full circumference of a single roller. Since I have 2 at approx. half warp, 11" is the ticket.

80 - 11 = 69. Half of this, or 34.5", is the center to center measurement for the rollers.

Then I needed to back out the balance of the roller diameter to get the distance between the ends of the rollers. this would be 3.5" total...1.75" x 2. This gives me 31" where the rollers are closest together. I'll be well above that point, so I'm planning a 32" bed.

[Shepherd]

Cant wait to see how it turns out.

[celeste]

May suggest you watch for surplus cast jig plate for a bed. It is ground flat and more stable then rolled. On the new market, it would be to expensive, but surplus, scrap price is the same for cast or rolled, and that sets the base price. You may know all this already, but maybe it will be useful to someone.

[Guitarnut]

Originally Posted by Shepherd

Cant wait to see how it turns out.

[Guitarnut]

Originally Posted by celeste

May suggest you watch for surplus cast jig plate for a bed. It is ground flat and more stable then rolled. On the new market, it would be to expensive, but surplus, scrap price is the same for cast or rolled, and that sets the base price. You may know all this already, but maybe it will be useful to someone.

Thanks. I wasn't aware of the difference. I have a piece of rolled plate on the way. I bought it from the same seller that I bought from to make my band saw table...it's been great for years now. I'll check the new plate and level it if need be.

Mark

[Guitarnut]

I added some additional bracing to the swing arm and added gussets to the lower table. Since I plan to radius fretboards on this sander, I want everything nice and square.

[adirondak5]

Great design work Mark , you make me wish for a Shop Smith

[Guitarnut]

I salvaged some bearings from lawn mower wheels last summer. The plastic castings on the wheels broke and wouldn't hold the bearings any more but the bearings are fine. The new wheels came complete with bearings so...

Four of them as luck would have it. Just a shade over .500" bore, and total diameter of 1.25". Going with direct drive, I don't need to worry about matching or adapting a shaft to the axles so .500" is great. The lip on the housing may prove to be useful.

I'm going to do a test to see if PVC glue bonds PVC to cutting board material. I have a 3/8" thick plastic cutting board that would be great for hubs. It would make machining housings for the bearings very easy.



Mark

[Guitarnut]

Originally Posted by adirondak5

Great design work Mark , you make me wish for a Shop Smith

Thanks Herb. I could see this easily adapted for a drill press using a right angle drive or even stand alone motor drive. The great thing about the SS though, is it's on-demand variable speed.

Mark

[Guitarnut]

I just ordered up a piece of .25" aluminum plate. It's already 6" wide...just need to trim to length. I also ordered a 2-pack of belts from Grizzly. 6" x 80" A100. I figured 100 grit was a good place to start.

I have a piece of scrap aluminum channel that I'll use to make the tensioner brackets. The rest,except for the swing arm, will be 3/4" MDF or 3/4" birch ply. Since I already have the ply and MDF in-house, I'm saving some bucks there.

Out of house costs so far are about $40. Though I did have to order a bi-metal band saw blade...so make that $48.

Mark

[Fred_Garvin]

Very cool (and too ambitious for me). Are you planning adjustments to the swing arm for compound radii?

[Guitarnut]

Originally Posted by Fred_Garvin

Very cool (and too ambitious for me). Are you planning adjustments to the swing arm for compound radii?

Thanks.

It will have settings for various radii but not compound. I think I would need to incorporate a u-joint of some sort for that to work. I haven't thought that far down the road yet. Great idea though.

Mark

[Guitarnut]

Well, just a bit of reading and it's apparent that PVC and Delrin don't bond well. So, I guess PVC sheeting is the best way to go. I've tracked it down in small quantities but it doesn't say whether it's solid or a foam core product.

Anyone know the answer by this definition?

PVC Type 1 Sheet, Smooth, ASTM D1784

Link



EDIT: It appears that ASTM D1784 is a standard for the material used in the production of rigid PVC pipe. ASTM D1785 is the standard for dimensions. It states that schedule 40 should be 3.5" OD and 3.0" ID just as HD states on the product specs for their pipe. Actually, the ID in the ASTM spec is 3.042" but who's counting thousandths.

I ordered the product linked above. 2 sqft for $16. Plenty for hubs and various other bushings as needed.

Mark

[Warnz]

Hi Mark

Sorry if you have already thought of this but it does not show in the renderings you posted...

I don't think the lawnmower bearings will do what you require from them. If the shafts are exactly 90 degrees to the C/L of the table they will probably be OK providing they are rated for the load applied.
As you say you will need the adjustment for the belt and this will apply an axial load to those bearings which they are not desinged for. You will need a set of "self aligning" bearings for the roller shafts and a flexible coupling for the drive as any adjustment of the drive roller will take it outside the C/L of the driveshaft.

Hope it all works out, as you can never have enough toys

Graham

[macaroonie]

Mark if you can fashion a roller with a very shallow barrel shape it will self center . The belt will try to ride on the high point of the roller as there is more tension therefore more grip / friction.

See pulleys on motors of belt drive turntables. . Some have a radical taper that changes the gear ratio, if you will, to help start up but once the platter is up to speed the belt will ride to the greater radius and then will stay there.

M

[Fred_Garvin]

Originally Posted by Guitarnut

Thanks.

It will have settings for various radii but not compound. I think I would need to incorporate a u-joint of some sort for that to work. I haven't thought that far down the road yet. Great idea though.

Mark

Leave it to me to start at the end and work backwards, but that's what got me thinking about using a belt sander to radius a fretboard in the first place.

One end would have to pivot from a different height relative to the sanding surface yet still remain square to the workpiece, i would assume. That's the part I'm having a hard time wrapping my brain around.

[guitarbuilder]

I had a crapsman 6 x 48 belt sander that wouldn't center on the top roller no matter how I adjusted it. I ended up building up a slight crown in the center of the roller with layers of masking tape. That worked for at least 20 years.

[celeste]

Originally Posted by guitarbuilder

I had a crapsman 6 x 48 belt sander that wouldn't center on the top roller no matter how I adjusted it. I ended up building up a slight crown in the center of the roller with layers of masking tape. That worked for at least 20 years.

That was a simple fix, didn't ever require duct tape

[Guitarnut]

Originally Posted by Warnz

Hi Mark

Sorry if you have already thought of this but it does not show in the renderings you posted...

I don't think the lawnmower bearings will do what you require from them. If the shafts are exactly 90 degrees to the C/L of the table they will probably be OK providing they are rated for the load applied.
As you say you will need the adjustment for the belt and this will apply an axial load to those bearings which they are not desinged for. You will need a set of "self aligning" bearings for the roller shafts and a flexible coupling for the drive as any adjustment of the drive roller will take it outside the C/L of the driveshaft.

Hope it all works out, as you can never have enough toys

Graham

Thanks Graham. It's not something I had considered. Certainly bears some thought. I just took off running with this idea and have yet to work out all the details. I'd be fooling myself if I thought I would get it right first try.

Mark