Purpose of motor cut out?

Justin Schmidt

Justin Schmidt

Joined
Feb 18, 2016
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Almost every new grinder out there has a motor cut out with a 56c from motor bolted to it normally off the ground. My question is What is the purpose of the motor cut out? Is it for perfect alignment? And why do makers always have them off the ground instead of just bolted down? Also if it is imperative to bolt the motor to the frame could i use a 5in bi metal hole saw? Sorry for constantly asking questions and probably annoying some. I just can't stop thinking about my grinder build and I want it perfect. Do it once and do it right.
 
I assume you are referring to the mounting plate for a face-mount motor?

Face-mount motors have a machined face that is perpendicular to the shaft, making it difficult (near-foolproof, but not idiotproof) to mount the motor out of alignment, assuming the machine has been built with the mounting plate correctly located. With a foot-mount motor, there is usually a certain amount of adjustment available/required to get the correct alignment.

If selling a grinder as a kit, without motor, using the face-mount means one less thing for the customer to louse up and complain about (cynical, me?). If selling a grinder complete, using the face mount saves the time needed to accurately align the motor.

If building your own, you can use either foot-mount or face-mount.

Several of the (European) kits I've seen use a foot-and-face mount motor. The grinder kit mounts to the face and the feet mount to the bench to hold the completed grinder down. This means there is no need to accommodate the holding-down system into the kit and keeps the kit relatively light and small for shipping.
 
I got ya. I'm planning on building my own and I've never used a 2x72 so I'm trying to do as much research as possible. The fool proof thing for customers makes a whole lot of sense. But if I'm building my own it's really not necessary If I'm understanding you correctly.
 
The reason is that all 56c motors fit the same cutout. If you need a new motor, or upgrade, all you need to know is that it is 56c.

If building a grinde from scratch, you could use anything you want ... but down the road you may want to make a change .. and you are locked into something other than the industry standard.
 
I like C mounts. One of my first jobs in machining was at Leeson turning C frame endbells on an old Mazak QT. IIRC we held the shoulder diameter to +0.000 -0.002". The face was square to the shaft because when turning the face of the motor, we held the endbell with an expanding mandrel in the bearing journal.

Anyway, a 5" hole saw won't do anything for you unless it's just for shaft clearance to use a frame mount motor. Here is a drawing of a 56 frame c-face mount, with a 5" circle drawn on center for your comparison. I guess axial location in a grinder like this isn't terribly important, only perpendicularity of the face to the belt pulley, so a 5" clearance hole would likely work just fine.

21cwhsn.jpg


The next grinder I'm building for reference:

141i3ch.jpg
 
as said, the motor cut out and mounting hole placement is industry standard. the mounting holes work for 56C, 143TC, and 145TC which all have the same shaft location. The difference is 56C has a 5/8" shaft while 143TC and 145TC have 7/8" shaft. once you get over 1hp, 143 and 145 frame motors are more common. there are enough folks making drive wheels in 7/8" that it should not be an issue.
 
valknut said:
Almost every new grinder out there has a motor cut out with a 56c from motor bolted to it normally off the ground. My question is What is the purpose of the motor cut out? Is it for perfect alignment? And why do makers always have them off the ground instead of just bolted down? Also if it is imperative to bolt the motor to the frame could i use a 5in bi metal hole saw? Sorry for constantly asking questions and probably annoying some. I just can't stop thinking about my grinder build and I want it perfect. Do it once and do it right.
Click to expand...

https://www.surpluscenter.com/_WebGraphics/CategoryImages/10-2699.jpg

What is the purpose of the motor cut out?
There is a lip there.
The cutout lets the frame fit flush

If you had a motor, or at least had looked at a motor; that would have been really obvious.

Try 4.5" holesaw
 
Dang, Count ... You are good!
I totally missed the question being about the cut-out size reason, not the why have it.
 
12345678910 said:
https://www.surpluscenter.com/_WebGraphics/CategoryImages/10-2699.jpg

What is the purpose of the motor cut out?
There is a lip there.
The cutout lets the frame fit flush

If you had a motor, or at least had looked at a motor; that would have been really obvious.

Try 4.5" holesaw
Click to expand...

Don't have a motor but I've looked at em online just never noticed that lip. That wasn't really the question I was asking anyway.
Kuraki that drawing helped thanks.
I guess what I'm trying to ask is why mount the motor like that instead of just bolting it down. But as its been stated. It helps with alignment for the customer.
 
Last edited:
valknut said:
Don't have a motor but I've looked at em online just never noticed that lip. That wasn't really the question I was asking anyway.
Kuraki that drawing helped thanks.
I guess what I'm trying to ask is why mount the motor like that instead of just bolting it down. But as its been stated. It helps with alignment for the customer.
Click to expand...

It's for alignment on industrial equipment built to use the standard dimensions.


"bolt holes" will be 1/32" oversize to allow clearance.
 
Makes more sense. Instead of having to worry about lining the drive pulley up and probably have something going wrong with tracking.
 
because there is no drive pulley. if it is a large motor, you may want to brace it up a bit just to help balance the grinder or hunt for the rarer footed 56c motor
 
Gonna resurrect this post. I'm picking up a 56c frame motor this weekend. And Ivery found a supplier for .500 steel for the frame. My question is what would be the best way to cut it with very limited tools (drill press and angle grinder) I sent the drawing kuraki posted to a machine shop and they wanted 20p bucks to cut it out. Is there a way for me to do It myself without jacking everything up?
 
On the Polar Bear Forge SlInG grinder, the motor facemounts to the upright and the base mounts to the foot plate. This is the ONLY thing that holds the base to the upright. You might not guess, but it is solid as a rock.
 
kdogmcg said:
On the Polar Bear Forge SlInG grinder, the motor facemounts to the upright and the base mounts to the foot plate. This is the ONLY thing that holds the base to the upright. You might not guess, but it is solid as a rock.
Click to expand...

It definitely looks solid. I'm just trying to find a way to cut a hole for the face mount and bolts. I've contacted Jamie to see if he could sell me just that piece of steel but it was a no go.
 
For anyone wanting to draft a grinder. Mcmaster carr has solidworks and cad drawings for just about everything for a grinder, including a 56c motor.
 
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