Thinking outside the box...a challenge!

[Teter09]

This forum has been a great source of knowledge for me. The number of active members contributing is always mind blowing to me. I'm hoping that I can use that to my advantage and get everyone in a big think tank for my issue.

I'm building a 2" x 72" belt grinder for shaping metal. Most of the homemade ones use a spring of sort sort to hold tension on an arm from below. I'm not really satisfied with that, it gives too much play and any stiffer of a spring and I'll need a 48" cheater bar or something to get enough leverage to torque it down out of the way to replace the belt (which is done often).

While working on something else I saw the ratcheting action of the PVC pipe cutters I was using. This made me think I could do this for the grinder as well! I've since learned this is done on a commercially available grinder, so the idea is sound. My issue though is finding the mechanism large enough to be useful for my purpose.

I'm very good at building things from parts, but I can't FIND the 'gear' in a large enough part in order to adapt. Effectively I'm looking for a piece of metal that is shaped like a 1/4 of a pie, with the teeth on the curved edge. I'm not sure what to call it other than the gear portion of the ratcheting action. It would need to be at least 5 inches tall (using the pie example, 5 inches on the straight edge, not the geared portion). Also, it doesn't have to be a Pie shape, a curved bar with the teeth on the outer portion of the curve would serve nicely.

I did ask the commercial maker if I could buy just that part from him, he recommended I just purchase his grinder (which I can't fault, but I've too much in my own currently to scrap it on one detail). I asked around to a few machine shops on having one made, and with prices of 100 - 200 for design and materials and all that, I thought I might be able to find a cheaper alternative.

Even if there is a cheaper option by dis-assembly of a tool I would be happy with that. Any ideas would be great, I appreciate the help!

 

[skipskip]

Buy a whole gear and cut it?

 

[Amitygravel]

Try Burr-King ,
The 960 uses that type of ratcheting tension adjustment.
You might be able to purchase the parts alone.
And of course we need pictures of the build and finished grinder.

 

[alan camby]

Here is a build picture of mine before paint. I just took the spring back to my table. The rod is just a bolt with a hole drilled in it. The bolt is threaded in a coupling nut for adjustment if needed. I don't have any problems with mine. Used the grinder today for about 15min.

 

[FMC]

car door window cranks?

 

[alan camby]

finished pic.

 

[loosewingnut]

Wow! That is an awesome looking grinder. Nice work.

 

[jtbinvalrico]

Nice work Alan!.......OP, in for results!

 

[Engineer61]

Instead of a spring, why not use a turnbuckle to tension the belt?
Also you should check out a Keith Fenner YouTube video where he is replacing bearings in his belt sander. It's a Wilton that uses two bolts, one to tighten the belt and another to adjust the tracking, and he gives you a pretty good look at how it's designed into the machine.

 

[AndyA]

The turnbuckle is a good way. I might add a break-over handle for quick release.

You could also use a cam and lever (like you might see on the lower wheel of an english wheel)

The turnbuckle+breakover is probably better since you can adjust for different belt lengths, or compensate for belt stretch.

 

[Mohawk Dave]

Yes...turnbuckle. We use them with Heim joints on the race cars. Suspension to alternator mounts. Infinite adjust-ability and uber strong. Much simpler and cost effective IMO.

 

[larry_g]

For the gear 1/4 look at the salvage yard for a flywheel that would have the proper radius for you and cut it up as needed. You could also use an air cylinder for a tensioning devise.

lg
no neat sig line

 

[Teter09]

What is a break over handle? I get the turnbuckle but can't figure out what that part is. I would need a quick release but since the swapping of wheels would change the slack I need to take out of the belt, not sure the turnbuckle would work well since it would be adjusted so often.

I like the thought of the auto window crank assembly. I hadn't thought of that route!!

 

[Mohawk Dave]

ok, just spitballin here, but if you are constantly changing wheels/tension, what about a tensioner on a threaded rod that spins (think lead screw on a vise) that you hook an electric/pneumatic impact to and hit the trigger. That's fast and easy on the back.

 

[Pumpman1968]

For the gear 1/4 look at the salvage yard for a flywheel that would have the proper radius for you and cut it up as needed. You could also use an air cylinder for a tensioning devise.

lg
no neat sig line

+1 'nuff said!

 

[larry4406]

Nice grinder. Link to plans and speed setup?

 

[darkk]

NICE! If I hadn't already gotten a KILLER DEAL on a Baldor grinder I'd be jealous as hell. Very nice grinder... After seeing this, I think I'd still build yours instead....

 

[W650Mike]

How about a serpentine belt tensioner?

 

[metaleltr]

How about a serpentine belt tensioner?

That is definitely out side the box. Not sure how well a sanding belt would hold up to the high tension. I guess you could position it so that it is near the end of the tensioning range. It would make belt changes easier.

 

[tarbellb]

Again, throwing stuff out there- but what about using a cam ratchet like you use on cargo and semi truck loads? Would that be to bulky? Or even a Come-Along ratchet mech?

Though after looking through all the suggestions the turnbuckle sounds like a very doable approach, you would just have to invest time into figuring out a good+quick way to adjust it.

 

[alan camby]

I don't understand the need to make it more complex than it needs to be. The belt tension is really set by how far the 1.5x1.5" square bar is moved away from the grinder frame.
IMO you need a spring in the design of some sorts. This assures that the belt is tight but not to tight. The shaft on the motor, at least on mine, is only 5/8". With a turn buckle, it would be easy to overload the motor and pulley bearings.
I can change belts and reconfigure the pulley setup in the mater of seconds. Push down the handle and the belt is ready to come off in less then a second. Why the need to ratchet and adjust things?
Watch how quick the belts and wheels can be changed on a KMG.

Mine has a frame kit from Polar Bear Forge. They have a web site.

Another option is the KMG. Every part can be bought from them http://www.beaumontmetalworks.com/

 

[GarageEnvy]

If we're trying to think outside the box, how about an old OMC outdrive. They aren't worth anything and most are broken. They have a partial gear and you might even be able to adapt the lift mechanism. Definitely not the simple way to go but it's outside the box.

http://www.ebay.com/itm/OMC-Stringe..._Accessories_Gear&vxp=mtr&hash=item19d6e63542

 

[kspwski]

What about replacing your spring with a pneumatic cylinder and hooking it to shop air with a valve. Vary the pressure to control the tension. Still get some "shock absorber" type action.

 

[KenS]

finished pic.

VFD and 3-phase Baldor!

Wow!

 

[Teter09]

I'm worried that truck ratchets or the turnbuckle would be too much. I believe some recommendations have been based on the ratcheting coming from behind the bar, like Alan's grinder has the spring. My spring is currently underneath the arm and its a compression spring between the upper tension arm and the tool bar holder.

I was trying to create something that would hold the tension arm up, like a support. That is where my mind was. I really like the idea of the Automotive window assembly, I think I can find one cheap enough. And if not, then my back up is the OMC drive. Unless anyone has any more suggestions?

That was the other issue, some of the ideas like the serpentine belt tensioner (while super overpowered) would also probably cost more than would be worth while to 'adapt' to my situation.

Alan, is isn't 'making it more complex than it needs to be' as you said. I have seen grinders which use a ratcheting action (like the TW90) in friends shops and when pressure is applied it didn't change how the belt tracked where as mine does slide one way or the other. When I was able to use a piece of rubber block to hold up the tension arm, mine didn't wiggle a bit! That is why I'm looking to add this. My NWG is simply my effort to build the best machine I can, and a larger compression spring won't get me the balance of tension yet ease of belt changing that I believe the ratcheting action would.

I will post pictures once it is done!

 

[jeremy v]

What about replacing your spring with a pneumatic cylinder and hooking it to shop air with a valve. Vary the pressure to control the tension. Still get some "shock absorber" type action.

That sounds like a neat way to do it for a permanently mounted belt sander in a place that has shop air. Changing a belt just involves bleeding off pressure at the sander and then reinstating full pressure again. If the belt was riding too tightly or if you wanted to sand a curve by having the belt more loose you could just dial the cylinder pressure down a little bit. That could also account for variances in belt length very easily. Interesting.

 

[AndyA]

The breakover handle is like the one shown. You can adjust the turnbuckle to set the tension. When you pull the handle (move left in the picture) it quickly releases the tension and give you a considerable amount of travel. When you push the handle (move right in the picture) it retightens the belt and goes right back to the same tension (assuming you haven't adjusted the turnbuckle). The handle "breaks over" center and sort of locks in the tight position.

The picture doesn't show how it works very well. I googled for pictures with the handle in both the tight and loose positions, but didn't find any. Ask more questions if this doesn't explain enough.

 

[Rico.]

There are some smart people on here... I'm afraid I cannot offer you some paradigm
changing engineering advise on your project, but I can help with your "quater of a pie,
with teeth on the curved bit" thing.

If my (old) brain is working things like this were installed in certain manufacturing machinary
and also in some automotive gearbox applications, and I believe they were called
Quadrant Gears.... Maybe a search would find you one to fit your specs... Good luck.

 

[Steve.S]

That was the other issue, some of the ideas like the serpentine belt tensioner (while super overpowered) would also probably cost more than would be worth while to 'adapt' to my situation.

I have a couple of Jeep serpentine belt tensioners sitting around if you decide to give it a shot. PM me if interested.

 

[Sureshot]

I am not following exactly what you are after but I once welded #40 chain to the inside of a 50" pipe so I could drive it with a sprocket. You could weld chain to whatever size pipe or plate as needed.

As for cam action I thought of the rubber hood latches on a semi truck.

Many belt driven items use the motor mounted on a hinge so the weight of the motor keeps the tension.

If you google "over center latch" you will also get a ton of ideas.

For big power we have used ratcheting boomers. We cut the chain links off and run 3/4" bolts through the eyes. If the handle is in the way it can be cut off and you can make use of the pawl assembly and turn the body with you hands.

Ratcheting bar clamp.

Hope this helps.

Very nice setup allan camby