Tool Post Grinder Build Motor Question

Thanks, Jake. I was afraid that was another rambling post.

Here's another route. The Workshop Practice series of books were available on .pdf in our forum library until someone felt hurt and complained that the deceased author's publisher sold the rights to a publication hoarding firm who isn't getting fair profit in exchange for the information, so they were taken down. Good news is I backed them up first. So here is the best writing I've seen geared toward hobbyists about making and baking spindles!

Microsoft OneDrive

1drv.ms 1drv.ms

You've got me thinking, obviously. I need a larger TPG for my big lathe, mine's a toy in comparison to one that can run wide wheels. Rather than spending a thousand or more on a ready-made tool, I could get a lot more bang for half my buck building my own. I also enjoy using my tools to make tools that I can use for making better tools. It's an Ouroburos, like Benzene (see pic)!

1024px-Ouroboros-benzene.svg.png​
 
Torque

How much torque does grinding need? Seems to me that if you need a lot, you’re probably being far too aggressive to get decent results. I’d expect dressing the wheel on a diamond to require more torque than finish grinding.

My expected primary use case is to shape annealed tool steal, hogging off most of the material by turning/boring, then hardening, then finish grinding for surface finish and precision.

I don’t think I’ll need much torque in my case. Sounds like you may have different needs and expected uses.

Accuracy

This is a topic I actually do know a little about.

Accuracy/precision/surface-finish comes mostly from the machine ways flatness and geometrical alignment, the spindle bearings (lathe and grinder) and geometrical alignment, avoiding lead screw backlash, how well the stone is dressed, and overall rigidity and isolation from vibrations.

I strongly agree that tenths over inches precision requires close attention to all these factors (but +/- 0.0002” over ~2” is about the best I ever
hope to achieve).

Either direct drive (router spindle) or belt drive (saw arbor with cheap DC motor) should be able to achieve high precision results. Belt drive might allow one to isolate more of the motor vibration in practice (unsure).

SFPM

You seem to want to design for large wheels for OD grinding and small points for ID.

Required RPM speeds are a function of wheel diameter, of course. It’s a lot easier to design a TPG if you minimize the difference between minimum diameter and maximum diameter wheels, especially if, like me, you are designing for two shaft speeds and belt drive rather than variable speed direct or belt.

The Dumore site gives recommended SFPM ranges for their stones on different materials.

Note that the work is turning, too, of course.

Design

As I said early in the thread, either direct drive or belt drive makes sense to me, but both seems weird. I’d make a hard decision one way or the other and stick to it.

I’d also suggest determining the minimum grinding point diameter you want to support and the maximum wheel diameter you want to support, then work out the RPM speed range you need from there. In practice, I think there is a LOT of latitude in SFPM, though, before problems arise.
 
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pontiac428 said:
Thanks, Jake. I was afraid that was another rambling post.

Here's another route. The Workshop Practice series of books were available on .pdf in our forum library until someone felt hurt and complained that the deceased author's publisher sold the rights to a publication hoarding firm who isn't getting fair profit in exchange for the information, so they were taken down. Good news is I backed them up first. So here is the best writing I've seen geared toward hobbyists about making and baking spindles!

Microsoft OneDrive

1drv.ms 1drv.ms

You've got me thinking, obviously. I need a larger TPG for my big lathe, mine's a toy in comparison to one that can run wide wheels. Rather than spending a thousand or more on a ready-made tool, I could get a lot more bang for half my buck building my own. I also enjoy using my tools to make tools that I can use for making better tools. It's an Ouroburos, like Benzene (see pic)!

Click to expand...
Thanks for that link!

I’ve been busy for a couple of days, but I’m back and thanks for the input once again.

I’ve decided to experiment more with my die grinder rig for now and get a better idea of exactly what I need. I’ve only used it once on a small project for which it did OK, but I know its limitations will be quickly reached. But at least I can feel out the process a little more before I make any decision as to how to proceed. Making a spindle will likely be the route.
 
Rex Walters said:
Torque

How much torque does grinding need? Seems to me that if you need a lot, you’re probably being far too aggressive to get decent results. I’d expect dressing the wheel on a diamond to require more torque than finish grinding.

My expected primary use case is to shape annealed tool steal, hogging off most of the material by turning/boring, then hardening, then finish grinding for surface finish and precision.

I don’t think I’ll need much torque in my case. Sounds like you may have different needs and expected uses.

Accuracy

This is a topic I actually do know a little about.

Accuracy/precision/surface-finish comes mostly from the machine ways flatness and geometrical alignment, the spindle bearings (lathe and grinder) and geometrical alignment, avoiding lead screw backlash, how well the stone is dressed, and overall rigidity and isolation from vibrations.

I strongly agree that tenths over inches precision requires close attention to all these factors (but +/- 0.0002” over ~2” is about the best I ever
hope to achieve).

Either direct drive (router spindle) or belt drive (saw arbor with cheap DC motor) should be able to achieve high precision results. Belt drive might allow one to isolate more of the motor vibration in practice (unsure).

SFPM

You seem to want to design for large wheels for OD grinding and small points for ID.

Required RPM speeds are a function of wheel diameter, of course. It’s a lot easier to design a TPG if you minimize the difference between minimum diameter and maximum diameter wheels, especially if, like me, you are designing for two shaft speeds and belt drive rather than variable speed direct or belt.

The Dumore site gives recommended SFPM ranges for their stones on different materials.

Note that the work is turning, too, of course.

Design

As I said early in the thread, either direct drive or belt drive makes sense to me, but both seems weird. I’d make a hard decision one way or the other and stick to it.

I’d also suggest determining the minimum grinding point diameter you want to support and the maximum wheel diameter you want to support, then work out the RPM speed range you need from there. In practice, I think there is a LOT of latitude in SFPM, though, before problems arise.
Click to expand...
Rex, thanks for the input.
Lot’s of good information to digest. I need some time to ponder it all!
 
After further experiments with my die grinder version of a TPG I recognized the importance of a proper spindle. On a whim I decided to search Craigslist for TPG’s and found a Dumore Series 44 that was purchased by an individual but never used. So now I am in the process of having the shipping arranged and look forward to having a proper TPG! The 44 has a limit of about 3” depth for internal grinding, but I think it will likely be enough for anything I may do. He also has a used series 57 available for sale, but it only has the external grinding spindle.
 
Sweet. I hope you got a good deal on it.

I'd be interested in any results you have to share. I'm not surprised the saw arbor didn't seem satisfactory, but I'd be curious if you actually acquired the router spindle and discovered any issues with it as well.
 
Rex Walters said:
Sweet. I hope you got a good deal on it.

I'd be interested in any results you have to share. I'm not surprised the saw arbor didn't seem satisfactory, but I'd be curious if you actually acquired the router spindle and discovered any issues with it as well.
Click to expand...
I never went forward with the saw arbor, but was using a small die grinder. I think the runout of the die grinder was too much for this application.

I wouldn’t say I got a good deal, but it is a fair deal. Selling new for $1942 and I got this one for $850, a nice discount off Dumore’s price. At least I know this is never used and the spindle is good.
 
I should also mention the following for anyone considering ordering from Dumore.

I ordered four small grinding wheels, the largest being 3" x 1/4". Total weight of all four wheels could not be more than 6 ounces.

When ordering from Dumore they put a "shipping hold" on your order to (in their words) ensure that you get the best shipping rate.

Well, they ended up charging me $31.18 for a box that totaled just over a pound (UPS ground lower 48 US)! What a rip off. I'm quite chaffed with that kind of gouging on their part. A few weeks ago I ordered a 9"x7"x10" cast iron angle plate from Shars. The box was twice the size of the box from Dumore and it weighed just over 20 lbs. $20 was the total for that.

Dumore also took over a week to ship from order date.

So just an FYI for anyone needing to get anything from them. Slow shipping and outrageous handling fees!
 
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extropic said:
One comment about the ER20 collet chuck: ER20 is 1/2" nominal max capacity. I wouldn't like to run a 6" wheel on a 1/2" shank.
Maybe think 3-4" for the OD work. YMMV
Click to expand...
This.

A 6” wheel is way too big for what you’re doing.
 
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