RKM556 Posted September 24, 2013 Share Posted September 24, 2013 Hello all! Just wanted some opinions as I have not been able to find any specific topics on this forum concerning the following. I am starting a larger project of building a KMG style 2x72 inch grinder for my knives, including interchangeable 10 inch contact wheel and a platen tools. I have a few plans picked out that I am going to pick and choose designs from, but if youi guys have any ones that have worked well for you, I would be very happy to hear about them. As usual, I do have a few questions though. I acquired a 3hp 230V motor, but it is three phase. I know absolutely nothing about electric motors besides the fact that it is apparently difficult to get one of these running. Is it even possible to do this cheaply or should I just go ahead and try to get rid of it for something a bit simpler? If I need to get rid of it, what's a reasonable price for a 230 or 480V 1750rpm 3 phase motor that presumably runs well? Along with this, is it reasonable to assume I can complete this project under 500$ if I have contacts who can machine the contact, drive, and slack wheels for me? Let me know your opinion if you gave build one of these before or have any tips. I do believe this tool will be worth the effort and I hope to build it solidly. Thanks for any and all of your help! Your friendly neighborhood blacksmith in-the-making, Ryan Quote Link to comment Share on other sites More sharing options...
jeremy k Posted September 24, 2013 Share Posted September 24, 2013 I did a very quick search in the forums with the search tool in the upper right corner of the page and found many threads about belt grinders /belt sanders/ 2x72 grinders etc -here's 1 - you can search the rest : Quote Link to comment Share on other sites More sharing options...
windancer Posted September 24, 2013 Share Posted September 24, 2013 I have a KMG and love it! I also have three Grizzly 2x72s that are good machines and I believe under $400 WITH the full 1 HP motor. You might want to give them a look-see before you get too far along :) Will watch for your build thred... Dave Quote Link to comment Share on other sites More sharing options...
Everything Mac Posted September 24, 2013 Share Posted September 24, 2013 I'm in the same boat. I know very little about motors and the three phase side if things was a bit confusing to say the least. Basically, assuming you don't have a three phase power supply in your shop then you need to get a converter to convert the single phase to three phase supply.http://en.wikipedia.org/wiki/Phase_converter You need an inverter to do this, sadly not cheap. You might get lucky and pick one up cheap on eBay. You can put a speed controller in this set up though which is quite nice. I don't know if this can also be done in single phase motors though I don't see why not... I got very lucky and was given a 3hp single phase motor. These are far simpler. It's just a standard wire that goes in, ie pos, neg, earth. I was told to run this with an RCDhttp://www.toolstation.com/shop/p99372?utm_source=feed&utm_medium=googleshopping&utm_campaign=googleshopping&mkwid=BLi4CAO0&pcrid=25046296943&gclid=CLyv2NDO47kCFQ_LtAod6Q0ApAhttp://wiki.diyfaq.org.uk/index.php?title=RCD I've been XXXXXXXXX busy with work so I've not got round to building anything more than this yet. As for the overall design there are hundreds to choose from. This thread is particularly helpful.http://www.britishblades.com/forums/showthread.php?60352-Let%92s-make-a-Grinder&highlight= All the best Andy Quote Link to comment Share on other sites More sharing options...
WayneCoeArtistBlacksmith Posted September 24, 2013 Share Posted September 24, 2013 You can use the 3 hp 3 phase motor if you get a KBAC 29 (1). I sell these for $476.26. Well, there goes your budget. I also suggest you look at getting my DVD on my web-site. Much simpler to build than a KMG clone. Depending on your scrap pile you can build this grinder for little over $1,000.00. Quote Link to comment Share on other sites More sharing options...
Dan C Posted September 24, 2013 Share Posted September 24, 2013 You might find this thread of some use to you. I've documented my progress though the project is currently onhold while I come up with wheels. I'm going with a motor from a treadmill which will give me variable speed. When completed I'll have ~$400 in this one. '?do=embed' frameborder='0' data-embedContent>> Quote Link to comment Share on other sites More sharing options...
rockstar.esq Posted September 24, 2013 Share Posted September 24, 2013 I looked into it for a while and quickly determined that I could get the Grizzly for far less time and money than building anything else. Now that I have it, I can say that it's plenty powerful and certainly capable of good work. It lacks speed control which is really expensive. Since it's a direct drive, you can't use pulley's without re-working the whole thing. I have been looking into variable frequency drives (VFD's) for it but I've found that one horsepower single phase motors aren't a common application for them. I haven't given up but it's not been an easy search thus far. Interestingly, I have found a bunch of VFD's that power a 3 phase one horse power motor with an INPUT of 120V single phase. That's pretty cool that they include the inverter function! http://www.automationdirect.com/adc/Overview/Catalog/Drives Until I'd used one, it hadn't occurred to me that the reason folks want to slow the thing down was to control heat. The finer the grit, the more surface area you've got contacting the work. At any given speed a finer grit generates more heat cutting. While I can hold a bar on the grinder for a couple of minutes with a 60 grit belt, I can only get a couple of seconds with a 2000 grit belt before it's too hot to hold. I'm still glad I've got the Grizzly - it's useful for sure. I'd probably get more done with a speed control since I'm forced to cool the work much more often in the finer grits. I'm not a professional so it's fine for hobby use as is. Still I'll post a cost effective speed control solution if and when I find one. Quote Link to comment Share on other sites More sharing options...
Robert Yates Posted September 24, 2013 Share Posted September 24, 2013 well I have to say the 2 X 72 KMG is the best there is I built a Clone and I am very happy with it I just finished up with wiring the shed up and my New KMG now has Life ( it has power Now and I am very happy ) Now to put it to work . Sam Quote Link to comment Share on other sites More sharing options...
rockstar.esq Posted September 24, 2013 Share Posted September 24, 2013 I just did a little more digging around on the whole VFD on a single phase motor and found a few tidbits worth passing on. The Grizzly belt grinder has a capacitor start motor. You can typically identify a capacitor start motor by the presence of one or more large semi-cylindrical lumps mounted to the motor housing. The problem with putting a variable frequency drive on a capacitor start single phase motor is that if you slow it down too much, you engage the start capacitor which can cause damage to capacitor, the drive, and/or the motor. Another problem with it is that at lower speeds, the torque is very low which is obviously not what's wanted with a tool. The cheaper models aren't really suited to a dusty, dirty environment. I've seen a few builds on line where folks installed the VFD inside a dust resistant enclosure. Computer case fans with filters help to keep things cool. A few things I didn't mention about the Grizzly is that they're not as precisely built as the KMG's, Burr Kings, Etc. There isn't an easy way to route the belt differently for smaller contact wheels. The stock 8" wheel doesn't stick proud of the motor case so you can't hollow grind stock longer than about 6" without hitting the motor. The 10" upgrade solves this problem but jumps up the belt speed which is it's own problem! Still it's about half the cost of most of the competition. Quote Link to comment Share on other sites More sharing options...
RKM556 Posted September 24, 2013 Author Share Posted September 24, 2013 Oh wow! Yet another bunch of replies. Lets get started. I did a very quick search in the forums with the search tool in the upper right corner of the page and found many threads about belt grinders /belt sanders/ 2x72 grinders etc - here's 1 - you can search the rest : Thanks you for that thread. I hadn't seen it before and it actually gave me a site to find a contact wheel for cheaper than I would have been able to get it. I have a KMG and love it! I also have three Grizzly 2x72s that are good machines and I believe under $400 WITH the full 1 HP motor. You might want to give them a look-see before you get too far along :) Will watch for your build thred... Dave See I would get a KMG, but 2,000$ or so is a bit out of my budget. Also, I have spent quite some time looking at the Grizzlys, and they just don't seem to match up to everything I'm looking for. Also, I like the idea of building my own. Andy, thank you for for the links. Now that I look into it, I think I'll be getting rid of that motor.... That grinder building link looks fantastic, also. I'm very thankful for all your help everyone. I am trying to make it along with scrap parts and such. When I get most of my supplies ready to be welded I'll start a build page! On a *completely* unrelated note, is anyone interested in a 3hp 1750rpm 3 phase motor? :D Quote Link to comment Share on other sites More sharing options...
windancer Posted September 25, 2013 Share Posted September 25, 2013 My Grizzly knife grinders all have the shaft out both ends- one for the drive wheel and one for a buffer or hard wheel. I redid the buffer shaft to a drive wheel and run pulleys for variable speeds. I can also run different size wheels in 6:, 8:, or 10 inch; Still not as much control as my KMG with the variable controller, but also not nearly as much money. I keep buckets of water under each grinding wheel. I always grind bare handed. The steel lets me know pronto when it starts to get hot and I just dip the knife into the water bucket and right back to the grinder. I will take a couple pics tomorrow and post them so you can see the setup. I understand that when you run 3-phase on 220 single phase there is a converter required that onlt powers two of the three legs. I have nothing in my shop that rune 3 phase. I have enough to think about already :) Dave I forgot about not being able to post pics here- If anyone wants them PM me your email address and I will send hem tomorrow. Dave Quote Link to comment Share on other sites More sharing options...
Zachary Posted September 25, 2013 Share Posted September 25, 2013 I just got done building one and so far am pleased with it I thought about trying to go the vfd route but decided it was to expensive and just used step pulleys instead and I actually like it quite well. I have a 7" serrated contact wheel a 2" contact wheel, a slack belt setup and a fixed platen setup. I also incorporated an 8" disk into mine as well. I think I have around 700.00 in mine. I'll try to get some pictures up so you can see it this evening if I can get time Quote Link to comment Share on other sites More sharing options...
rockstar.esq Posted September 25, 2013 Share Posted September 25, 2013 Windancer, I'd love to see pictures of your setup - it sounds really cool. Quote Link to comment Share on other sites More sharing options...
homeshow Posted December 23, 2013 Share Posted December 23, 2013 One of the guys over here at the Choo Choo Forge built this little beauty last week. Yes I will be copying it next week Quote Link to comment Share on other sites More sharing options...
vapremac Posted December 23, 2013 Share Posted December 23, 2013 Keep us updated on your build. Three phase electric motors are not as "scary" as everyone makes them out to be, its just the unknown particulars is why everyone shys away from them. Actually they are far more efficient to operate in terms of the cost of electricity, using less amps than a single phase motor of comparable horsepower. They have a much longer life span because of the fact that less heat is built up inside of the housing due to less amperage draw. Three phase motors can be run from single phase 203/208/220/240 in two different ways, one being a static type converter, which is the cheapest way, but cuts the HP rating of the motor in half, hence a 5hp becomes a 2.5hp, reason being the microfarads are not up spec on the third leg. The second method is the use of a rotary phase converter, which by far is the best method. Standard single phase input and a capacitor bank to bring up the voltage on the third leg and no drop in HP rating as long as the dependent motor HP is not larger than the parent rotary phase. I build rotary phase converters and have quite a few customers who power two or three machine tools with three phase motors all simultaneously from one 5 or 10 hp RPC. For one three phase motor used intermittently a static convertor might be the more cost effective approach though. Quote Link to comment Share on other sites More sharing options...
homeshow Posted December 24, 2013 Share Posted December 24, 2013 I sourced all of the metal for my build at Seaton metal in Athens Tn. It was all scrap cut offs at $0.25 per pound. I also found 3 12 foot pieces of cold rolled 1/4" X 1 1/2" tool steel. Given the yellow ends and spark test I'm thinking 1095 or something around that. I'll be using the mystery metal testing in the knife section of IFI. I'm tempted to go back and get the rest 20 or so more new unused 1/4." X 1 1/2" steel. Best 25 cents a pound for 140 pounds of steel. Quote Link to comment Share on other sites More sharing options...
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