2 X 48 Belt Grinder (again)

[rwm]

I started on my belt grinder!
I built this motor from scratch from scrap bin parts. I think it looks OK, although the capacitors are a little big. (Yes I know it reminds you of your ex but please refrain from commenting.)





Specs are 3/4 HP @ 3450 RPM. Already blows 15 amp circuits.
It's a start.
Robert

 

[rwm]

Just some crude ideas while waiting for material.



Not sure how to make the platten yet. Perhaps just like the table although it really doesn't need to be adjustable. What material?
How much spring tension?
Need to find appliance feet.
I'm torn about using a lever arm or an eccentric axle (like Mark did) for the tracking wheel. How much do these belts stretch over time?
I am thinking of crowning the top pulley only, not the drive pulley. Any ideas on that?
R

 

[Mark_f]

Just some crude ideas while waiting foNot sure how to make the platten yet. Perhaps just like the table although it really doesn't need to be adjustable. What material?
How much spring tension?
Need to find appliance feet.
I'm torn about using a lever arm or an eccentric axle (like Mark did) for the tracking wheel. How much do these belts stretch over time?
I am thinking of crowning the top pulley only, not the drive pulley. Any ideas on that?
R

I have been told you can crown either pulley but not both. I don't know if that is true so I chose to crown the drive pulley ( because my store bought 4 inch was that way). I have a set of plans for one that uses a lever instead of the eccentric shaft. I chose the eccentric shaft because it did not require welding.
Also, I have never had any belts stretch.
As far as material, I used aluminum because I had it but the frame needs to be at least 1/2 " thick to prevent flexing. Steel can be thinner, like 1/4". ( learned that the hard way)

 

[rwm]

Thanks Mark! Very helpful info.
R

 

[strantor]

This won't directly answer any of your questions, but it will illustrate how a belt grinder can be made in a total vacuum of science and attention to detail. It's a belt grinder I made a few years back out of scrap. I didn't crown any pulleys or machine any eccentric axles or measure any spring tension. I used an old bent rusty ruler to adjust tracking, bungee cords to adjust tension, and a plastic golf back wheel to drive it (roller skate wheels for idlers). It works just fine, gets the job done.

https://www.google.com/url?sa=t&sou...IIGzAA&usg=AFQjCNF8y99YcykjxoY_QdNRtJjJeQE3nA

I admit it is the epitome of a kludge and it's on my list to do over. Now that I have machine tools in my arsenal I can do a much better, professional job. But it's just hard to find time to reinvent something that already works just fine.

Point is, don't over think it.

 

[rwm]

"...but it will illustrate how a belt grinder can be made in a total vacuum of science and attention to detail." I love the way you said that! That is a remarkable grinder! I think there is more science built into your design than you are giving yourself credit for. Still, I get your meaning.
I like the design process as much as building a tool and I hate that feeling that I could have done better. I am an optimizer! I like the collaboration here and always appreciate everyone's ideas even if I don't use them.
I hoping my grinder will be fairly heavy duty so I can hog away steel.
Pulley stock. (also Ice Press stock)


This will give me a 4" drive pulley and a 2.5" crowned tracking pulley.

R

 

[Chipper5783]

It looks like you are going with direct drive? That will yield a belt speed of about 3700 fpm. Have you considered a belt drive, so as to increase the belt speed (with the added benefit of getting the motor bump out of your way)? It will be interesting to see what comments you get on target belt speeds for different applications.

My recollection is that to really hog the metal off, you should push the belt speed to about 6000 fpm.

 

[rwm]

Yes, about 3700 SFPM. I thought that would be adequate but you may be correct. I considered the belt drive but dropped it in favor of the 3450 rpm motor. Hmmm...maybe too slow. A 5" wheel will get me up to 4500 SPFM which seems better. Couldn't you have told me this before I ordered the stock?
R

 

[Mark_f]

You should be fine with the 4" pulley. I run a 1750 rpm motor which gives about 1850 sfm. that speed works great. I found running the belts too fast shortens their life dramatically. I checked with a manufacturer and they said the best speed was around 2500 sfm for best belt life. That is my opinion and findings. I'm sure there are many different opinions out there.

 

[rwm]

I made some progress...then disaster.


Top pulley finished. The bearings fit nicely. The large stock is for the drive pulley.




So after facing and machining a boss I drilled the center hole enlarged it to 9/16 and tried to ream it to 5/8. Here is my setup for reaming.


The problem is that the reamer began to chatter (more like a vibration) immediately. I tried slower and faster with the same results. Now I may have messed up the bore of this pulley possibly beyond salvage.


Someone please help! What am I doing wrong to cause this chatter. The reamer is securely fastened in the tailstock and I used plenty of cutting oil. The reamer itself is new. It is not damaged even after this anomaly. I was running at 500 and 750 rpm. I should have just used a darn drill or boring bar ! I want to understand why this didn't work?

R