2×72 Belt grinder frame question

[Suzuki4evr]

Hi there.

I am busy getting parts ready to build a 2"×72" belt grinder. The design is simple and you probably saw it lots of times before. It is basically going to look like the pic below.


I was just wondering if there is a reason for the two or sometimes three platen ram slots (see pic below). Is it just for more stability or can you just weld the one tubing straight ontop of the feet tubing? I don't mind doing two slots, I just want to know if there is a good reason for this. Can someone shine some light on this?


Thank you in advance.
Michael.

 

[ddillman]

I don't know but it looks like you could use all three positions

 

[Suzuki4evr]

But for what reason?

 

[rabler]

Typically two so that the belt goes around one as pictured, and a second to hold an adjustable rest. Mounted separately so that you can adjust the belt tension and the tool rest position independently. Not sure why you'd want a third.

 

[mikey]

But for what reason?

one slot is to hold the platen and a seond slot is to hold a work table or rest.

 

[Suzuki4evr]

That it explains it. Thank you

 

[Suzuki4evr]

Will this gas shock suffice for the tentioning the belt? It is about 170mm long extended. The other option available was 120N this one is 80N.

 

[rabler]

I used a 60lb rated gas spring, that translate to 267N. While the 60lb is fairly heavy, my gut feel is 80N (18 lbs) is too light. A big factor is how much leverage the gas spring has on the tensioning arm. I have slightly more than 2:1 pulley to strut as you can see in the CAD view above. Obviously there is a leverage/travel trade-off.

Here's a link to a belt manufacturers article on tension:

 

[Suzuki4evr]

May I ask,why would one need so much force resistance?

 

[rabler]

The gist of the link above is if the tension is too low you destroy the belt because it slips under high load. If I read it right, 30-50 lbs in the belt for a 2" wide belt. With a 60 lb spring I'm at the low end of that given a 2:1 advantage on the tensioner arm, especially after you factor in the belt angle over the tensioner pulley.