DIY 2x72 belt grinder--how much spring tension?

A

Alfazulu

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Mar 24, 2016
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I'm in the process of making a 2x72" belt grinder. It is somewhat based on the DCKnives online plans. However, I didn't like the way the tension wheel is just mounted atop a vertical post. I figured an arm, like a Bader, would make for easier belt changes. I also saw a production grinder with a gas shock instead of a spring. I figured I'd try that out. I went to Advance Auto Parts and found a cheap on with holes at each end (that you can run bolts through). There were only a couple there that had holes instead of the ball-and-socket attachment.

Anyway, this thing is STIFF! I'm estimating it at 100lbs of tension. Is that going to be too much? It may be too much for me, as the whole point of the arm was to gain leverage over the spring and make belt changes easier. It seems like I have lost that advantage. With this much tension, I worry about breaking belts, wearing wheels/bearings, and so on. What do you think? Is there a better source for such a gas shock? I couldn't find any info on the packaging about how much pressure they exert.

Here are some pics so far. I'm waiting on wheels/belts to come in, and will buy a motor this week. I'm hoping to have it done by the weekend.

IMG_0339.jpg
 
Look up "Gas Struts" on McMaster-Carr site. Tons of options including some that are adjustable. Or check out your local bike shop for a used air shock from a full suspension bike. That's what I used. It is totally adjustable. I only have 30 Lbs in my shock on my home made 2x72
 
Up to 100lbs but after building 1 grinder and using it for a while my second grinder will have the ability to adjust it in a range of 30-90 lbs. The higher tension really helps with tracking but makes using felt belts or nonwoven like scotchbrite, a pain, as they end up stretching further than you have travel in your tracking/tension wheel.
 
I want to know the answer to this question too .But , did you take into account the point where gas shock push the lever ? I mean the forces that act is dependent on the point where pushing ? /distance from the lever shaft and point where is set gas shock /
 
Thanks guys! Great info. Natlek, yes, I took that into account. I put the shock closer to the pivot point so I would have more torque over it, and it's still just brutal. The further from the pivot it is, the greater the torque it would exert on the belt. I couldn't have put it much closer. I'm just going to take this one back and buy one that is right. Thanks again guys!
 
Whats most important is that the build is true and straight. 25/35 is all the tension needed.. Too much tension will just wear everything out.. Originally I was going to use a strut. But settled on a pull spring. Works great.



Pedaling
 
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