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New 2x72 Grinder


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Just wanted to share this. One of my good friends is a engineer who after finally finishing his some 10 years in college, decided to open a machine shop.

I had off hand mentioned I wanted a grinder, but couldn't find any that I thought were affordable. He offered to make me one for next to nothing mostly to test his process and make sure it was up to snuff.

He mostly worked on it during his down time and well, its nearly done! What are your guys thoughts? I think he did a dang good job. Granted, it still needs guards and such but its 90% done.

Uses a 1/3 hp variable speed motor with custom variable speed control he built. 1750 rpm and ~3600 sfpm. Frame is Hiwin linear rails that were no longer usuable for CNC applications. The rollers and other misc parts are 3D printed and filled with granite epoxy.

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Looks like he built a woodworking one and not a metalworking one.  I see neither a platen nor a contact wheel and 1/3 hp is WAY underpowered. I would suggest they look at plans created by people who have experience using them.  1.5HP is suggested!  How is the belt tensioned for quick changes?

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Interesting design.  A couple thoughts though.  If it has a belt tracking adjustment I didn't spot it in the photos.  The variation in belts makes that a necessity.  Secondly you will need a flat platen, but I assume there is a plan for that.   Most importantly, that is not nearly enough HP for a 2x72 belt grinder.  You really want to be in the 1.5 to 3 hp range if you plan to do any real grinding.  I stalled a 1 hp motor frequently with moderate pressure before I upgraded.

Looks like TP beat me to it and with pretty much the same issues.

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The belt tracking and such has yet to be put on. Its what he is working on today. This was kind of just the "shell". The platen has yet to be put on as well. He was curious if the motor would be up to par with it. Once he gets the rest done and can test it, he has other motors on hand to swap with. He may have done calcs based on a 3 phase motor which to my understanding has a little more oomph behind it. Ill have to ask.

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Keep in mind that the size of the drive wheel makes a big difference in speed and power.  The bigger the drive wheel the greater the speed (surface feet per minute), but the lower the effective power. Normally you see drive wheels in the 3 to 5 inch diameter range even with 2 or 3hp motors powering them.

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The belt tension system I believe he said isnt on yet either. I believe he said he is going to have the upper wheel utilize the rail to slide up and down to apply tension and allow quick and easy changing of the belt.

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I relayed the concerns you guys laid out to him and he is making a few design changes. He is going to test the motor and see how easily is stalls out then swap it if needed. I slightly jumped the gun on the completion. I guess it is only roughly 60% complete and not 90% as he still has a decent bit of stuff to do :blink:. I believe he said he took inspiration from Grizzly and their models and set rpm/fpm based off Red Labels website which states hard and hardened steel is between 1560-2940 fpm. I looked and they also list carbon steel as 4920-8820 fpm. Should he had shot for that one?

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I know he looked at various brands before coming up with his basic design then modified it based on what I planned to use it for as well as the space in which I had to use it and mount it. I don't remember what his focus in engineering was (I just remember the broad electrical-mechanical), but when I mentioned it he said he had enough motors and misc. parts laying around he could probably build one. Would give him a project to test his various equipment and such on as he is just starting out.

If memory serves, his focus was more in robotics. He interned at the Honda plants not far from my town and maintained their welding line robots. Not that that is really relevant I suppose.

 

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Two main ways of designing a new version of an existing product: One: review all currently on the market as to features and manufacturing difficulties of those features to come up with a design that provides the most for the least.  Two, the more difficult way, is to do a deep dive into requirements and come up with ways to meet them "de novo"; aka re-inventing the wheel. Often derided, but it's how we got from iron tyred wooden wheels to pneumatic wheels!

Research on the web is not a good basis for either method IF you don't have the experience to judge which findings are true and which are bogus.  The 1/3 hp is a dead giveaway that something was wrong!  (If it wasn't a TEFC motor that would be another.)  Contact wheels allow for fast grinding, hollow grinding and fullers. A good design IMNSHO  should allow their use and preferably their interchangeability.  My Bader has contact wheels from around 3/4" diameter to 10".  It also has positive tracking in *both* directions---very nice. (I've used grinders where you turn a bolt to track one way and have to loosen the bolt and bump the arm to get it to go the other way.)

Note slack belt grinding can be handy too depending on how you want to use it. 

Most grinders I have seen are based on the: Bader, Burr king and Square Wheel grinders.  Checking out what professional knifemaker supply companies sell might be a way to narrow down what is needed.  (Note you are looking for belt GRINDERS and not belt SANDERS!)

This sounds like a Dunning-Kruger incident where if you don't know anything about a field you don't know how much you don't know.

 

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Would you the say his current design is flawed then and needing a total rework? I did iterate the motor issue to him and he is looking through his "pile" of motors and seeing what else he has to swap it out.  If his current design is just a wash I want to let him know before he puts more work into it lol.

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What I would say is that they don't know enough about what a knifemaker needs their grinder to do and how to figure out how to do it.

I sure wish Kovals was still out on the east side of Columbus so you could stop by.  Perhaps he could visit Adlai and see his set up?

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Have you linked or given him pics, drawings, plans of existing 2" x 72" belt grinders? Do you know which are good designs and which are so so grinders? 

Give the guy a chance and heck yourself too. Wheels need reinventing on a regular basis but you have to have an idea of what it does and how it works.

Frosty The Lucky.

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Yup when we were brain storming the design I had sent him links to Grizzly and beu...something for ideas. After he looked over those we started taking into consideration my work space and how I could mount it. We decided completely vertical would be the best fit for my limited space, and it would mount on the left of my bench and hang off the side.

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I have used the Grizzly and it will do the job, just not as versatile as the Bader, KMG, and most specialty knife grinders. I would have been happy, if I had a friend who was willing to reinvent the wheel for me so to speak. Give it a chance and remember it can be modified as you gain more experience.

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  • 3 weeks later...

More design progress! The backplate (not sure what the actually technical name is) has already been made and installed. Next is the work deck that should be attached today.

Confirmed with my friend that the tensioning system works via the threaded rod and the top wheel. Using the knob allows the wheel to be moved up and down for quick tensioning and belt changes. He was able to stop grinding an item and change the belt out very quickly. He tested the tracking and it tracked beautifully. 

After more testing, we upgraded to a 1HP motor but it still bogs down a little bit when applying a lot of pressure to really hog off material with the 40 grit belt.

Edit:

I know you guys had mentioned the right HP for the motor, but 1HP was the biggest he had laying around. I am hoping to try it out and if it still is a problem, I will have to purchase a higher HP and send to him to be modified/fitted to the machine. Still trying to use what he has laying around and is free :D.

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Why when they remodeled the building next door at work I went to the scrapyard and grabbed all the newer motors; Dayton 1.75 hp,  TEFC, pristine, US$10!.  Gonna use that one for my 25# LG, one of the smaller ones is allocated for building a tumbler.  Good ones are $OUCH!  nowadays if bought new.

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I did mean used. I don't want to shell out for a brand new motor :lol:.

New or Used, I still have to take it/ship it down to him since he has to modify the housing and such to mount the monstrosity he built to it.

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Old motors could be huge. I have an old 1.5hp motor from another powerhammer that is 6-8 times the weight of the new Dayton I just mentioned.  The motor place told me to  replace it with one 1.5 times  the hp if I wanted to go to a new motor as the old large ones had really great torque with the larger size.

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