# Can't Understand What A Tool Post Grinder Is Good For?



## great white (Apr 12, 2015)

Yup, noob alert question.

I've been looking at tool post grinders (specifically, the older atlas catalogs) and I can't figure out what a tool post grinder is good for.

Isn't it just another way to do what you already can with HSS/carbide cutters?

Except that it makes a bigger mess?

Please help me to understand what and why you would use a tool post grinder attachment.


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## Billh50 (Apr 12, 2015)

I have used my tool post grinder for making stepped pins out of already hardened drill blanks. I have also used it a couple times to get a real nice finish on material that just would not allow me to get a good finish with normal turning. I have used cut off wheels on mine to put grooves in for "C" clips or snap rings on hardened shafting.
They do have some uses. Just not everyone will need one.


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## pdentrem (Apr 12, 2015)

Just be sure to cover the ways as much as possible. The metal dust and grit from the wheel will get into and under everything.

You can think of the tool post grinder as a poor man's cylindrical grinder. Instead of 0.001" now you can achieve 0.0001" or better on some machines. To get that diameter just right, like when sizing shafts for bearing fit OD or ID. Refinishing valves for an engine.
Pierre


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## planeflyer21 (Apr 12, 2015)

/\/\/\ Yup, exactly what Pierre said.

I've not used a toolpost grinder but have done work on ID and OD grinders, to be held to 0.0002" tolerance on size and 0.0001" of taper end-to-end on an 8" part.


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## samthedog (Apr 12, 2015)

My advice for what it's worth, is get an old junker lathe, and add a toolpost grinder and leave your accurate lathe clean.

If the part is unhardened, I have seen pretty good results achieved by angling the compound so that you can sneak up on the dimension ever so carefully, which eliminates the need for tool post grinding. If the part is already hardened, then you need to grind.

Paul.


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## great white (Apr 12, 2015)

Ah, so I guess I get the hardened materials part. Although I would think carbide would be the go to for that. I can see how it might allow you to do hardened materials on a smaller lathe (ie: less powerful) though.

But I'm not understanding the "accuracy" part. Would not the grinding wheel "erode" as it traveled along a surface during a cut? Wouldn't this introduce and error like a taper?


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## Bill Gruby (Apr 12, 2015)

The accuracy part is simple. There is no tool flex. The grinder produces a much better and closer tolerance finish.

 "Billy G"


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## RJSakowski (Apr 12, 2015)

samthedog said:


> If the part is unhardened, I have seen pretty good results achieved by angling the compound so that you can sneak up on the dimension ever so carefully, .......
> 
> Paul.


If you set your compound at 5.74 degrees, you get a 10x expansion of your crossfeed dimension. I.e., a .001" movement of compound is equivalent to a.0001 on the cross feed.


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## JimDawson (Apr 12, 2015)

great white said:


> .....
> But I'm not understanding the "accuracy" part. Would not the grinding wheel "erode" as it traveled along a surface during a cut? Wouldn't this introduce and error like a taper?



The grinding wheel does erode but at a rate much less then you might expect and only on the leading edge of the cut.  To illustrate this, here is a picture I took of a surface grinder in action.  This wheel has already made a couple of passes across this plate and has removed about 0.030 off of the top and the wear on the wheel is only about 1/4 inch from the leading edge since being dressed.  The rest of the wheel is still in it's dressed state and untouched.  The cross feed in this case is right to left in the picture, and the depth of cut is about 0.005.  I turned the coolant off momentarily to snap this picture.  The wheel is 2 inches wide and all of the work is being done where you see the sparks.


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## pdentrem (Apr 12, 2015)

One thing to realize is the surface finish will be will much better compared to regular turning. Think of it as surface grinding on the lathe. It is all about fit and finish.
Pierre


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## great white (Apr 12, 2015)

Ok, I think I'm getting a bit better handle on the concept. 

Since I typically only deal with aluminum/mild steel and my tolerances are not "uber" critical, its beginning to sound like I don't really have need of a tool post grinder. 

I may make one though as I will have a nice 1/8 HP motor when I convert my Atlas to DC. Might be a nice project to practice on....


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## tertiaryjim (Apr 12, 2015)

A   1/8 hp motor will only serve for very small wheels and light grinding.
Would work well for a small internal grinder with 3/8"dia. and smaller stones.


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## great white (Apr 12, 2015)

tertiaryjim said:


> A   1/8 hp motor will only serve for very small wheels and light grinding.
> Would work well for a small internal grinder with 3/8"dia. and smaller stones.


Since its going on an atlas 10F and will not get any heavy use, that sounds just about right to me.


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## mattthemuppet2 (Apr 12, 2015)

an extra part to the accuracy thing (according to what I've read anyway, no personal experience) is that grinding doesn't leave any grooves or marks on the work like you get with turning, even with a slow feed or large nose radius. So when you measure your OD, that's what it is, you're not measuring the peaks of a turned piece which may later collapse or wear away and reduce the OD. I've never worked to that accuracy nor needed to, but others do need it for their application.


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## pdentrem (Apr 12, 2015)

One thing I did notice is with a ground surface that runs on a bushing, if one does not polish to remove the microscopic peaks left by the wheel, the bushing will not last.
Pierre


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## John Hasler (Apr 12, 2015)

mattthemuppet said:


> an extra part to the accuracy thing (according to what I've read anyway, no personal experience) is that grinding doesn't leave any grooves or marks on the work like you get with turning, even with a slow feed or large nose radius. So when you measure your OD, that's what it is, you're not measuring the peaks of a turned piece which may later collapse or wear away and reduce the OD. I've never worked to that accuracy nor needed to, but others do need it for their application.


You are still measuring on the peaks between the scratches left by the abrasive particles.


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## mattthemuppet2 (Apr 13, 2015)

interesting, I was under the impression that any marks left by the grinding wheel were of a much smaller magnitude than those from turning


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## JimDawson (Apr 13, 2015)

John Hasler said:


> You are still measuring on the peaks between the scratches left by the abrasive particles.





mattthemuppet said:


> interesting, I was under the impression that any marks left by the grinding wheel were of a much smaller magnitude than those from turning



While that is true, normally a properly ground surface is an order of magnitude smoother than the best turned surface.


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## fgduncan (Apr 13, 2015)

I'm not sure that you want to be using a grinder on aluminum. My (limited) experience is that the stone gets clogged pretty quickly and makes a very poor finish.  Steel works just fine. Might get some of the more knowledgable/experienced guys to comment on using a grinder on aluminum.


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## great white (Apr 13, 2015)

Grinders intended for ferrous metals aren't used on aluminum, unless something has changed that I don't know about.....


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## Billh50 (Apr 13, 2015)

We used to grind some aluminum plates and blocks at a place I worked. If done properly with right coolants or a light oil it doesn't clog up the wheel that fast.


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## f350ca (Apr 13, 2015)

Had to resurface the mounts on my chucks on the Colchester I bought. The tool post grinder is the best option for work like this, the intermittent cut from the keyway would have made it impossible with a cutter.






Greg


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## Wobbles (May 25, 2015)

great white said:


> I may make one though as I will have a nice 1/8 HP motor when I convert my Atlas to DC. Might be a nice project to practice on....



Agreed, nice project.  But in the end with such a light-duty unit you may wish you had simply bought a Dremel Tool and the tool post adapter.


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## chips&more (May 25, 2015)

Wow, what an interesting thread. So many opinions. I would like to input a few. A tool post grinder is just that, it grinds. A big difference when comparing it to the cutting action of a tool bit. Hard materials, interrupted cuts, surface finish, tolerance control to name a few are jobs for a grinder. A 1/8hp motor should be able to handle 2” diameter stones. Aluminum can be ground, but I would not do it all day, the stone will eventually load up. Frequent stone dressings (coarse) would be a top priority. IMHO a Dremel is not in the caliber of any tool post grinder, and one that is properly homemade. AND the most important of all, protect your lathe from the grinding grit/swarf. I would wrap the lathe with an easily tearable material, like newspaper. And when you are done, just to make sure, give your lathe a good cleaning. If you have or can find a tool post grinder for your shop, I would say definitely get it. When you need it, there is no substituting…Good Luck, Dave.


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## Mark in Indiana (May 25, 2015)

I used to reface silicon covered rollers (for transfer printing) on a lathe with a TPG.


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## aeroHAWK (May 26, 2015)

I have made molds for injection molded plastic parts out of 7075 aluminum. I ground the aluminum blocks on my surface grinder using a soft, open wheel and lots of coolant. I also smeared a layer of grease all over the surface before each pass. It made a real nice flat parting line - much nicer than any flycutter. The wheel didn't load up very fast at all. The biggest problem was the magnetic chuck wasn't strong enough. 

I have also refaced silicone covered rollers with a toolpost grinder for a printer friend of mine....


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## WoodBee (May 26, 2015)

Hi all,
I have read all postings in this thread, very interesting.
I agree my question doesn't apply to everyone, but none the less:
I am in the process of "restoring" a universal grinder which has a cylindrical grinding attachment. If that is operational, would there be any advantage in also having a toolpost grinder for my lathe?
(agreed, it is a nice project to build, but I still have some of those left  )

Peter


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## ezduzit (May 28, 2015)

A toolpost grinder should find many uses for making or re-purposing shop tooling. For example re-grinding slightly larger tooling to fit machines with obsolete tapers, like the #9 B&S on my Index vertical mill. Not much tooling around to fit. but plenty of larger tooling that can be re-ground.


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## battlewagon (Jul 6, 2015)

Years ago when I worked in a print shop we used a tool post grinder to sharpen the cylindrical knives used to slit the paper as it went into the printing press.


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## mohamer (Jan 8, 2021)

If you want to try the Dremel on a tool post mount, the Flex Drive that I have fits my 1/2 inch Boring Bar Tool Post Adapter very well.


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## Grinderman (Jan 8, 2021)

mohamer said:


> If you want to try the Dremel on a tool post mount, the Flex Drive that I have fits my 1/2 inch Boring Bar Tool Post Adapter very well.
> View attachment 350331


Is there a trick to getting the rubber outer cover off of the flex tool? I took the two screws and front cap off but it won't come apart. What do you do for the spindle lock button?

Edit: got it apart but you must have left the tool intact and just peeled off the outer rubber cover?? Is that a Dremel flex tool?


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## Tozguy (Jan 8, 2021)

The flex tool shown is the older model that did not have a rubber outer cover. It is used as is.
And, the spindle lock is a hole that you have to insert a 1/8'' pin in to hold the spindle. The hole is visible in the knurling adjacent to the chuck.


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## Grinderman (Jan 8, 2021)

That makes sense, thought I was missing something. Newer model is quite different.


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## mohamer (Jan 8, 2021)

Sorry, mine is like me, an Antique...


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## Tozguy (Jan 8, 2021)

Antique but not obsolete.


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## ericc (Jan 8, 2021)

I made one for just one use; making a custom sized drill bit with a 1/8" shank.  Worked great.  Spent more time cleaning up afterwards than grinding.


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## macardoso (Jan 8, 2021)

My understanding is that a toolpost grinder has light duty but extremely accurate bearings to allow it to achieve the tolerances that are desired. A dremel or home brew tool with cheap bearings will work but maybe not as accurately.

I think the limitation of the toolpost grinder on a lathe over a true cylindrical ID/OD grinder is that you are still cutting with the machine's inherent inaccuracies (like bed twist and taper). A purpose built cylindrical ID/OD grinder will produce more accurate parts more easily as it is built to a higher class of precision than a lathe.

All that being said, if I found a reasonably priced unit, I'd jump on it.


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## LynnEdwards (Jan 8, 2021)

I bought a used Themac tool post grinder on EBay for $400 back when EBay had good stuff to buy.  I bought it to recondition/sharpen  punch and die sets which I also bought on EBay.  The punch and die listing said it was about 400 lbs total - I ended up getting over 2000 lbs of assorted punches and dies (Pexto/Whitney/DiAcro style).  The seller kept apologizing over and over that the shipping was going to be a little more expensive because of the added weight.  I had no complaints - I kept 280 punch/die sets for myself and sold on EBay about 100 more.  I made all my money back plus another $3000.

The Themac tool post grinder had a masking tape note on it when I got it.  It said "Not for sale June 1960".  It disintegrated when I touched it.  The tool post grinder works great!  I've used it a lot.  Besides the punches I used it to resurface the brake rotors on my wife's car.  They got pretty badly scored which I first tried to clean up on my lathe with standard carbide cutters.

Has anyone tried that?  Maybe my machine is just not robust enough, but I couldn't cut into the brake rotor with HSS or carbide. All it did was skim along the surface and squeal a lot.  Brake rotors are hard!  I was a little reluctant to "dig in" with a lot of force since I worried about an 8 lb rotor working itself out the lathe chuck and bouncing around the garage.

My tool post grinder came to the rescue..  It ground the rotors down without any problems.

The other thing I noticed about the Themac tool post grinder is that the design hasn't changed since 1960.  It looks identical to new ones being offered today (for a lot more money).  Well, except for the guard - mine didn't come with a guard so I had to make one.  It seems incredible to me that even in 1960 they didn't see the need for a device that can spin up to 40000 RPM.

Lynn


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## LynnEdwards (Jan 8, 2021)

chips&more said:


> Wow, what an interesting thread. So many opinions. I would like to input a few. A tool post grinder is just that, it grinds. A big difference when comparing it to the cutting action of a tool bit. Hard materials, interrupted cuts, surface finish, tolerance control to name a few are jobs for a grinder. A 1/8hp motor should be able to handle 2” diameter stones. Aluminum can be ground, but I would not do it all day, the stone will eventually load up. Frequent stone dressings (coarse) would be a top priority. IMHO a Dremel is not in the caliber of any tool post grinder, and one that is properly homemade. AND the most important of all, protect your lathe from the grinding grit/swarf. I would wrap the lathe with an easily tearable material, like newspaper. And when you are done, just to make sure, give your lathe a good cleaning. If you have or can find a tool post grinder for your shop, I would say definitely get it. When you need it, there is no substituting…Good Luck, Dave.


Chips,

I totally agree.  I see people guarding their ways with cloth.  This scares me.  If the cloth gets caught up in the spinning work it could be a disaster.  But newspaper (or other thin paper) has never worked for me.  If you're doing a lot of grinding the swarf builds up and starts the paper on fire.  Then I'm left with the decision to finish the pass, or start fire fighting.

I've always found old beer carton cardboard works better.  It doesn't catch fire as easily.  I always seem to have a lot of it around anyway ;-).

Lynn


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## e189552 (Jan 14, 2021)

I used a Dumore grinding setup to grind bearing journals on all C-5 nose landing gear.


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## Shotgun (Jan 27, 2021)

mohamer said:


> If you want to try the Dremel on a tool post mount, the Flex Drive that I have fits my 1/2 inch Boring Bar Tool Post Adapter very well.
> View attachment 350331


I was going to make an adapter, but this makes the most sense for a home shop.  The shaft can be removed, then both the holder and the flex shaft can be used for other tasks.  Just ordered a shaft from ebay for $18.


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