Surface Ft / min for belt grinders -

[DHarris]

Ok, title pretty much says it all.

What is the optimum SF/min for a belt grinder? Want to optimize for HSS tool grinding, but will put step pulleys on to change higher / lower for other uses.

Thanks for reading / inputs

Dave Harris

 

[Uglydog]

I did some online searching when I was working through powering my 6x48 BS.
I just found that I had saved the results. Here is what I have with associated sources.

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Delta 6x48 Sander Motors and Pulleys
Modified on 2009/04/25 15:11 by jayeson Categorized as Electrical, Restoration Topics, Sanders
» Delta 6x48 Belt Sander » Delta 6x48 Sander Motors and Pulleys
http://wiki.vintagemachinery.org/Delta6x48Motors.ashx

Motor Sizing¶
From the 1936 "Delta 6" Belt Sander" publication{Reference:http://www.owwm.com/mfgindex/pubdetail.aspx?id=1873|Delta 6" Belt Sander}: "It is inadvisable to install less than a 1/2 h.p. motor in a unit of this size, and a 3/4 h.p. motor with double V-belt drive should be employed if very heavy sanding is to be done. Only a constant speed, repulsion-induction motor should be used." With the quality of modern V-belts, a single belt drive should be sufficient. Earlier motor horsepower ratings were more conservative than today, especially for repulsion-induction motors. Late model sanders were supplied with a 1.5 hp induction motor.{Reference:http://owwm.org/viewtopic.php?t=16336|Delta 6x48 belt sander motor size}

Pulley Sizing¶
From the 1936 "Delta 6" Belt Sander" publication{Reference:http://www.owwm.com/mfgindex/pubdetail.aspx?id=1873|Delta 6" Belt Sander}: "With a 1725 r.p.m. motor, the pulley recommendations are 5 in. for the motor and 4 in. for the sander, giving a belt speed on 3100 feet per minute. This is a good all-around average for general work, and is as fast as the belt can be operated for woodworking without glazing or burning." For a 3450 rpm motor, simple math suggests a 2-1/2" pulley however the 1985 parts list calls for a 2-3/4" pulley. {Reference:http://owwm.org/viewtopic.php?t=27788|6x48 sander gearing? Quick question!} Alternatively, the band saw calculator may be used with Band Wheel Dia. set to 5.5 in. You are looking for a SFPM of 3,100.

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Daryl
MN

 

[DHarris]

Thanks Daryl, I've read everything from "you want slower - e.g. 1750" - all the way up to 5000!

Great references!

Dave

 

[Buffalo20]

My Jancy RadiusMaster, a 2” x 48” belt grinder, is about 3600 sfm, that removes large amounts of metal, incredibly quick (and if careless, the end of fingers, finger nails and knuckles down to the bone, in an instant). There is times I wish the speed was higher, but I’ve never had any desire to slow it down. If I want a slower speed, I’ll use my 6” x 48” Delta/Rockwell.

 

[mikey]

Ok, title pretty much says it all.

What is the optimum SF/min for a belt grinder? Want to optimize for HSS tool grinding, but will put step pulleys on to change higher / lower for other uses.

Thanks for reading / inputs

Dave Harris

Dave, I've never seen a SFM reference for grinding hardened tool steels with a belt sander. Much depends on the type of belt, grit and whether you're grinding M2, cobalt or tungesten. I can give you some thoughts based on working with a belt sander in this application for some years:

• Grinding tool bits requires power, with a minimum of 1/2HP.
  
• Belt material makes a BIG difference. I've used aluminum oxide belts for years but the new ceramic belts I just tried are significantly better. I can now grind a cobalt tool faster and cooler than I could grind an M2 bit with an AO belt; this is a bigger deal than you might think.
• My motor runs at a fixed 3450 rpm and runs a 42" belt. This is great for shaping and medium finishing but if you want to go with finer belts then slowing the belt down would be better; this means a variable speed motor. I don't have that option so I finish with an 80 grit belt and hand-hone from there. If I ground tools for an income then I would run to finer grits.

I think the ideal belt sander for tool grinding would be a 1.5 - 2hp variable speed 2 X 72" belt sander with a precision tool rest and a ceramic glass-lined platen. This would allow you to alter the speed to the phase of the grind; fast to shape, slow to finish. I don't believe nailing down a specific SFM is all that important; you'll figure out your speed requirements fairly quickly.

If you can find an old Sears 2X42 belt sander, model 351.215420, grab it. It has a squarish shaped motor and was made in Taiwan. My only regret about this sander is that I didn't buy three when I had the chance.

I have the 1/3hp version of this grinder also and it is still available from other sources - Palmgren and others. It is an anemic grinder but I wonder if it would be suitable if I used a ceramic belt. I plan to try it soon and report on it. If it works for grinding lathe tools then that would be an economically attractive option for hobby guys.

 

[DHarris]

Thanks everyone,

Mikey - I have a 3/4 hp motor sitting around - will use drive belt / 2 step pulley (1 : 1 & 1 : 2) so I can have 1725 / 3450 options on speed. Due to current bench space limitations, I'm going to stick to a 2 x 48" belt size (but machine can also work with 2x42 if there is a grit that I want in one & not available in the other). If this works out - then I'll look into making it a 2 x 72 in the future. As the wheels are the same between the two sizes (only add one more wheel for the 2 x 72) I'll not waste $$. Also looking for a larger motor as well.

will let you know how it goes.

p.s. The grinder table that I mentioned to you earlier was a design by Harrold Hall - - - he has a simple one and a complex one. Will make an adaptation of the two I think - - still thinking about it for now. Ultimately would like a table that has a tilt mechanism with a measured scale - thinking small worm gear / lead screw??

Dave Harris

 

[Cobra]

I run my 2X72 at about 5000 SFM for grinding steel.

 

[DHarris]

thanks Jim.

 

[mikey]

Thanks everyone,

Mikey - I have a 3/4 hp motor sitting around - will use drive belt / 2 step pulley (1 : 1 & 1 : 2) so I can have 1725 / 3450 options on speed. Due to current bench space limitations, I'm going to stick to a 2 x 48" belt size (but machine can also work with 2x42 if there is a grit that I want in one & not available in the other). If this works out - then I'll look into making it a 2 x 72 in the future. As the wheels are the same between the two sizes (only add one more wheel for the 2 x 72) I'll not waste $$. Also looking for a larger motor as well.

will let you know how it goes.

p.s. The grinder table that I mentioned to you earlier was a design by Harrold Hall - - - he has a simple one and a complex one. Will make an adaptation of the two I think - - still thinking about it for now. Ultimately would like a table that has a tilt mechanism with a measured scale - thinking small worm gear / lead screw??

Dave Harris

Accu-finish has an interesting approach to setting table angles. They use a simple protractor on one side of the table frame; you can set it to whatever angle you wish. The sliding table is able to pivot and lock at whatever angle you need. In use, you set the protractor to the desired setting, bring the table over the protractor and set the table on top of the protractor and lock the table angle and slide the table over to begin grinding operations. Quick, simple, reliable and very accurate. No screws.

 

[DHarris]

Is this the table you were talking about? I've been looking at that one, but was thinking how to make the "T" handle geared in some way to turn to the angle easily and then have the upper "pin" have some type of lock nut / lever to hold in place. Base plate would obviously be different as this is designed for their machines..