jack620 15th March 2011, 09:25 PM I'm in the market for a new or used pedestal grinder and I'm lucky enough to have a 3 phase outlet in my workshop. However I'm not sure whether to go 3 phase or single. I don't own any 3 phase equipment yet.
What are the advantages of 3 phase machines? I think I read somewhere that you get more torque for a given HP. I guess there is no start capacitor or centrifugal switch to fail either.
It will be used for general grinding and occasional sharpening of tools. I may even fit a polishing wheel to one side. Should I opt for a lower speed like 1420 RPM or just go for the standard 2850 RPM? Is it worth spending the extra $ on a 10'' model?
I've seen Chinese made 8'' & 10'' 3 phase grinders advertised. Do any of you guys own one of these or know anything about them?
Appreciate any advice.
Bushmiller 15th March 2011, 10:07 PM [QUOTE=jack620;1290676]
What are the advantages of 3 phase machines? QUOTE]
Grunt:wink:.
With bench grinders, 1 HP 240V motor comes up to speed in about 3 -4secs. 1 HP 415V motor comes up to speed in about 1 sec. I guess it comes down to torque. Given a choice I would go for 3 phase any time.
Regards
Paul
Cliff Rogers 15th March 2011, 10:34 PM If it was me, I'd save the 3Ph outlet for a table saw our a big lathe & just use a single phase grinder.
It has been argued that the slower grinder is better that the faster one, particularly if you are grinding other than HHS.
jack620 16th March 2011, 08:28 AM Thanks for the replies. I already have a single phase 3 x 3HP combination woodworking machine. I'm looking at a lathe, but it will probably only be C4 size and the ones I've seen are all single phase.
I'm not sure what HHS is. I'll be grinding most of the common metals, plus sharpening 'hard' stuff like woodworking chisels, knives, etc.
Cliff Rogers 16th March 2011, 09:41 AM I meant HSS high speed steel.... tool steel that doesn't get upset if you get it a bit hot just as long as you done plunge it in a bucket of water while it is hot.
bollie7 16th March 2011, 10:34 AM If it was me, I'd be looking around for a good used GMF or similar 3ph rather than buy a new Chineese single phase. Unless you need to do a lot of heavy grinding, a 250mm or larger grinder might be a bit of overkill in a home workshop.(also expensive when it comes to "new wheel" time) A 200mm would be ideal for just grinding tools ( by "tools" I mean lathe tools etc) and general purpose workshop grinding.
check these out
Macbro 12inch double ended pedestal grinder, 3hp (Type A Asset) Auction (0011-570073) | GraysOnline Australia (http://www.graysonline.com/lot/0011-570073/manufacturing/macbro-12inch-double-ended-pedestal-grinder-3hp-type-a-asset)
GMF double ended pedestal grinder, 200mm, 240 volt (Type A Asset) Auction (0025-570073) | GraysOnline Australia (http://www.graysonline.com/lot/0025-570073/manufacturing/gmf-double-ended-pedestal-grinder-200mm-240-volt-type-a-asset)
bollie7
Bushmiller 16th March 2011, 11:04 AM It has been argued that the slower grinder is better that the faster one, particularly if you are grinding other than HHS.
Cliff
As they are all induction motors, speed is only affected by the number of poles or the gearing. I think I am right in saying that bench grinders are direct coupled. Therefore a two pole motor will give a speed of,say 2850rpm, while a 4 pole will give 1440, 6 pole 960rpm ect. irrespective of whether they are single phase or three phase.
Having said all that............. the slow speed grinders may commonly be available only in single phase. I know that carbatec have a selection. Pedestal grinders may be available in a variety of speeds because they are often belt drive. I suspect (but don't know) that the primary reason for this is to suit the diameter of the grinding wheels.
A lot is going to depend on the end useage. I have seen some experts say to use the fast grinder for primary sharpening of tools. Just be a little more patient to avoid removing the temper:wink:. (Sorry about the pun).
Regards
Paul
Cliff Rogers 16th March 2011, 02:27 PM Cliff
As they are all induction motors, speed is only affected by the number of poles or the gearing. I think I am right in saying that bench grinders are direct coupled. Therefore a two pole motor will give a speed of,say 2850rpm, while a 4 pole will give 1440, 6 pole 960rpm ect. irrespective of whether they are single phase or three phase.
..........
Preaching to the converted here.... it was Jack who asked the speed question in the first post.
Bushmiller 16th March 2011, 03:30 PM Preaching to the converted here.... it was Jack who asked the speed question in the first post.
Sorry Cliff. Forgot to look back and took your comments out of context. Over to you Jack.
Regards
Paul
jack620 16th March 2011, 07:06 PM Yep, thanks fellas. I understand the relationship between poles and RPM. I was more interested in the practical application of the different speeds that are available.
I think I'll keep an eye out for a used GMF or similar on EBay or Grays. I don't think I'm going to have much choice over the speed or number of phases. There just aren't that many to chose from.
Bushmiller 16th March 2011, 08:01 PM I think I'll keep an eye out for a used GMF or similar on EBay or Grays. I don't think I'm going to have much choice over the speed or number of phases. There just aren't that many to chose from.
Remember the add-on costs with Grays. Buyers premium and GST if you are collecting, but also delivery and some other charge if the goods are sent. In any event the final cost always seems to cost about 20% more than you paid. Just factor it in.
Good luck
Regards
Paul
jack620 16th March 2011, 08:54 PM Thanks Paul, will do.
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