Recommendation? QUESTION: Benefits/advantages of variable speed belt grinder?

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Mikel_24

Basic Member
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Sep 19, 2007
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2,959
Hello all,

Long ago I put together a belt grinder. Direct drive, single phase, fixed speed (33m/sec belt speed if I am not mistaken). Works great even though a few things could be totally improved (may do it in a near future).

The thing is that I have a spare 3kw three-phase motor and I was thinking about putting it in my belt grinder along with a VDF. It could be almost a bolt-in replacement (it will fit with little to no modifications).

The VDF needs to be single phase input - three phase output and suitable for 3kW. I do have a 3phase service (380v) but I would like it to have single phase input, just in case I move it to another location with no 3ph. I only need the speed control feature, I don't need any more bells and wisthles but anyway I guess a VDF like this is not going to be cheap.

So, after all this babling... the question is: What benefits do I get from a variable speed grinder? What speeds are used with which type of belts and for which materials?

Besides knife making, I use it also for general fabrication (hobby stuff, I don't make a living on that).

I use my belt grinder mostly for mild steel, some stainless, some aluminum, the ocasional wood (I also make wooden spearguns and sometimes shape the stock with the grinder), home made micarta and stuff like that. I have noticed that with wood I sometimes get burn marks and I think that running the belt at lower speeds may result in a better finish. What about polishing?

Other than that, is it really worth the trouble or should I stick to my current setup?

Thanks!
 
Cost/benefit ratio is always something each person has to decide whether not it’s worth it. I started on a grinder that ran wide open-the belts ran really fast. When I ended up getting my own and put a VFD on it, I was very happy with it.

For ME-I gain more control in my grinding with the ability to slow things down. Mistakes can happen very fast when grinding on blades. That potion of the knife making process is still the most stressful for me. Having the ability to slow the belts WAY down when I want to helps with the stress. It also just makes doing some detail work that much easier when the belts are running slower. I RARELY run my machine at full speed now. I just don’t need it going that fast. And when the changes in the steel/wood/micarta, etc happen a bit slower, I can see a mistake that’s taking shape faster and stop it from getting worse a lot sooner. Not much makes me more frustrated than to have a lot of time into a project only to see I messed it up beyond saving on the grinder...

Jeremy
 
There is no comparison to using a VFD vs a single speed grinder. My first grinder was a 3 speed belt drive and thought that was all that was needed. I "finally" got around to building another grinder with VFD and WOW - what a difference. "IF" money is a concern, even in Spain you should be able to order a VFD from China for $100 USD or so. It will be a NEMA 1 enclosure and will need filters over the air inlets, or have VFD mounted inside a box to protect from metal dust. If money is no object, then order a VFD with a NEMA 4x enclosure.

You'll wonder why it took you so long to go VFD drive once you do.
 
gudspelr said:
... I can see a mistake that’s taking shape faster and stop it from getting worse a lot sooner...
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Jeremy, that's exactly one of the reasons I was expecting.

Ken H> said:
.... "IF" money is a concern, even in Spain you should be able to order a VFD from China for $100 USD or so. It will be a NEMA 1 enclosure and will need filters over the air inlets, or have VFD mounted inside a box to protect from metal dust. If money is no object, then order a VFD with a NEMA 4x enclosure...
Click to expand...

The way you mention it sounded like I lived in a third world sh&$hole country! :D:D:D:D

Money is not a concern... to some extent. The control box of our car lift just broke and we found a replacement on our equivalent to the US Craiglist that included the control box + 3kW motor. Soooooooooooo... the original 3pH motor (perfect working order) it is free for me to use. The original motor does not have a plate, so I will just assume it has the same specs as the new one (fitted in the same kind of car lift).

I have no trouble spending 100-150€ in a VDF but I don't use it that much to justify expending +300€ in a top-of-the-line one.

I take good note of the NEMA ratings you mention! Thanks a lot!

We have a metal working forum here in Spain that works fairly well. I think I am going to ask there which would be the most suitable VDF for me. Those guys buy VDF's by the docen to power industrial 3ph equipment in their garages for hobby stuff.

Mikel
 
Variable speed on a belt grinder is ALWAYS worth it. You can ruin stuff real quick with a belt moving fast. When sharpening or doing belt finishes on knives, after heat treat, l turn the speed way down once I get past the metal removal grits(anything above 60 grit gets run slow). You have so much more control when the belt is moving slow. When you’re doing finish work, this is invaluable.

Sharpening to an exact angle is very easy on a belt grinder, as you can use a fixture/jig, and tilt the platen to the desired edge angle. But if you don’t have variable speed and can’t turn it down real slow, then it’s really not worth the risk of burning the edge. Which will happen at speeds above 1750rpm, at the very apex of the edge. Even though I can turn my grinder down until it’s running super slow, I still add water to the belt and wet grind my edges. I also let the platen cool down before sharpening and dunk my blade after every pass. Sharpening is one of the last steps in my process and I’m damn sure not trying to ruin a blade at that point.

Get the VFD, you’ll be glad you did. I have NEVER heard someone say that they regretted getting their vfd.
 
Go vfd. I very rarely use it at 100%. Try moving up to a 2500 grit belt at 100% and see if you don't blow your ht
 
Maineiac1 said:
I have a VFD single phase 115 in, 3 phase 220 out with a nema 1 enclosure. Rigged my own filters and only cost me about $150 USD.
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Thanks for the suggestion!Problem is that the one linked is for 1HP... and my 3PH motor is... 3KW which is roughly 4HP. Talk about prices going up exponentially!!!

JG Custom Metal Works said:
Variable speed on a belt grinder is ALWAYS worth it. I have NEVER heard someone say that they regretted getting their vfd.
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Enough said. I think that after all the feedback I will be getting the VDF for sure.

Kali4nia said:
Go vfd. I very rarely use it at 100%. Try moving up to a 2500 grit belt at 100% and see if you don't blow your ht
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I don't even have belts that fine! But my thinner ones (soft backing) pretty much snap first try if I use them with the platen. And I guess it has something to do with the belt speed as well....

Thanks!
 
Mikel_24 said:
The way you mention it sounded like I lived in a third world sh&$hole country! :D:D:D:DMikel
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Ooops, sorry I did NOT mean it to come across meaning Spain is a third world country. It's been many years since I was in Spain. I have lived in Guatemala and that country can be hard to find material and parts in. Spent time in Thailand, Mexico, Brasil, and a few other countries that were hard to find material in. Many folks just don't realize how good parts are to find here in USA. BUT - since we get so much stuff from China, it's available most anywhere in the world {g}

I've got this VFD and have been very pleased with it: https://www.ebay.com/itm/232789984198? While is link is for shipping from USA, I'm sure you can find it in China or perhaps even in Spain.

Ken H>
 
Ken H> said:
Ooops, sorry I did NOT mean it to come across meaning Spain is a third world country. It's been many years since I was in Spain.
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Don't worry, I was just messing with you a little bit. ;);) I know you didn't mean it the wrong way

Actually I am quite lucky as well since I live in the north of the Spain (Bilbao full blown industrial region) and I work in an engineering company so if I wanted a name brand device I could probable even source it locally with a step discount :D

Ken H> said:
I have lived in Guatemala and that country can be hard to find material and parts in. Spent time in Thailand, Mexico, Brasil...
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I fully agree, those countries are a totally different animal.

Ken H> said:
I've got this VFD and have been very pleased with it: https://www.ebay.com/itm/232789984198
Click to expand...
Looks good and it is rated for 3kW, just what I was looking for! Greeeeeeat!
 
12345678910 said:
NEMA ratings are USA

Look for the metric standard IP66
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Thabks for pointing it out. The tests for each rating are slightly different but that could be a fair equivalent. Also most of the manufacturers who intend to sell devices worldwide try to get them certified in both systems.

Let's see what I can find.
 
It’s a whole new world with a Variable speed grinder . As others have said I rarely use the full speed unless I want to hog off a lot of steel with a 36 grit belt. Also I grind my bevels & taper tangs after heat treatment and things can hot real fast with full speed.—————————Also the finer the belt, the slower I run all three of my grinders. ———————————————————Each maker will have his own sweet spot of speed for each grit depending on what they are doing, Finishing steel, Sculpting handle materials, etc.. Try it! You’ll like it!
 
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