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rob45
07-06-2011, 12:14 PM
Rob,

Recently my friend Rex asked me a question in another thread to which I can only speculate on the answers, at least as far as our grinders are concerned.

The question concerned the use of a contact wheel as a drive wheel. He wanted to know why people always use a solid wheel instead.
For background on the question and my response, please refer to posts 53-55 in this thread: http://knifedogs.com/showthread.php?18552-Newbie-Flat-grinding-help&p=170484#post170484
In my response, I stated that I had no experience concerning his particular application, but listed potential design hurdles.

In 1996 I built a stroke sander to speed up production. This was used for cabinet doors, metal panels, etc.
This machine was a 2-wheel design with a 5 HP motor. It used a 6x186 belt, with a sliding table and sliding lever-operated 6x12 platen.
The wheels were contact wheels sourced from another parted-out machine.
Although it was one of my larger "backyard engineering" projects, the machine was a pretty sound design, and saved me over $3000 vs. buying one.
The problem was that whenever pressure was applied, the belt would slow and eventually stop moving if enough pressure was applied. The motor was definitely not the issue, and adjusting tension did not help.
I pulled the cover off to see what was going on while an employee put it under load. The tire itself was losing grip on the wheel.
After much frustration, I had a solid wheel built, and had no problems after.

I know there are a few designs on the market that successfully combine a contact surface with the drive. I believe you even offer it as an option on your grinders. Also, there are many individuals who successfully use the concept when doing a belt conversion on their surface grinders.

What are your thoughts on this?
1. Is it a case where a tired wheel behaves differently when pressure is applied against it? (e.g., surface grinder conversions, actually using the wheel as a contact surface.)
2. Is it possible that tired designs have their limitations, but for our applications we are well within those limits?
3. Directly related to above question, perhaps my above experience was unique. The lever-operated platen was capable of generating tremendous pressure over a considerably larger surface area than is typically seen, and something had to give?
4. Maybe I simply had a defective wheel? Or perhaps an incorrectly-designed wheel for that particular application?

Any insight you may be able to provide would be a tremendous help.
Regarding machinery with "tires", my experience is very limited. I have built a few bandsaws, a sawmill, and a few different sanders.
For the saws, I can visualize how the blade tension would counteract any tendency to slip.

I do not wish to provide inaccurate information to Rex, as this may very well be a case where question #2 above applies.

Thank you,
Rob

mike miller
07-06-2011, 03:03 PM
I have a grinder that was built by Jerry Braggs in I believe Pasadena , California sometime in the 70s or 80s. The only other one I have seen is used by Lloyd Pendleton. It is a three wheel ,drive and grinding wheel are tired ,and the other one is aluminum. The drive wheel is 8 inch and the grinding wheel is 9 3/8. It has a ratched bar that the grinder wheel is mounted on and you push it out to tighten the belt then lock it in place by lever. It has a two HP motor reversable and the motor pulley is three speed with a 4 speed pulley on the drive shaft.
I leave it on the low speed whihc is 800RPM for finish work. i now have a ten inch wheel mounted to grind hollow grinds.