Poor Man's Tool Post Grinder

KeithB

Well-Known Member
#1
I had a job come up that required drilling a 0.2" diameter hole into an aluminum part. The problem was that the hole was on the side of a rounded surface and required spotfacing to make a flat surface to start the drill in, otherwise the drill would wander off and not be accurately located. I could have used a 5mm end mill but none were available locally and I didn't want to wait for 2-3 days to get one so I improvised.

Years ago I had need for a small tool post grinder to grind a bore in a part on my manual lathe. I have a full size tool post grinder but it is a big, bulky, and heavy affair complete with a large 110V electric motor, a 6" wheel, frame, etc. I decided to make a tool holder for a pneumatic hand grinder. This was so long ago that I do not have pictures of the machining process to make the tool holder, but it required a milling machine to make the tongue and then a lathe with a boring bar to cut the interior surface to a curve that matches the OD of the grinder. The grinder is held in the tool holder with worm clamps.

It doesn't have a lot of power, you can't hog off material, and the wheel wear has to be dealt with, but for some things it is just the ticket. I found a used 1/4" HSS end mill (the end was still sharp but the corners and OD was worn) and chucked it up in the collet chuck. With the lathe running in reverse (to oppose the grinder's rotation) it only took a couple minutes to turn each end down to about 0.204". The mill will no longer cut sideways but it does great feeding straight down to mill a flat spot to start a drill.

I don't know if this will spark anyone else's ideas, but I can certainly see some uses for something like this doing gunsmithing work.

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KeithB

Well-Known Member
#3
Just for reference. The guys that normally make the parts (and who subbed the job to us) made the part on the left. We made the part on the right. They said it was OK to use a #5 center drill (3/16" dia tip) to start the hole and then drill to size. I think their part is ugly and while their customer says it is OK I wanted to conform more closely to the print specs. Note that the square slot on the front of the pieces is .380" by .750" and is cut in 6 passes with an 1/8* end mill spinning at 5,000 RPM. The design engineer specced a .030"R corner, which would require using a 1/16" end mill. NOT! The customer OKed using an 1/8" end mill, which worked fine, we cut 210 pieces and never even dulled the tool enough to change part dimensions.

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Brad

Administrator
Staff member
#5
A tooost grinder is one of those tools that isn't often needed but when it is nothing else will do. I would like one but the cost can be prohibitive.
Nicely done Keith. Your part looks far neater and that counts.
 

Brad

Administrator
Staff member
#6
Am I the only one who noticed that Keith's rule may be prone to intense interrogation? I don't want to run afoul of that rule.
 

Ian

Well-Known Member
#8
I think Brad was referencing the initials and the Russian thing that we'll never hear the end of until some current terms expire.

That's not a cheap tool post grinder, that's a carefully machined, custom shop-made tool adapter! I didn't take pictures of it, but I had what I call a "white-trash" tool post grinder set up to enlarge the neck on a Lee collet neck sizing die for some special brass Fiver and I were messing with. The neck of the hardened collet needed to be ground at a slight taper even with the collet fully closed in the lathe chuck (to account for brass springback being more near the shoulder), so I trammed the original taper angle of the collet neck with a test indicator mounted to the compound to set the compound angle, clamped a Dremel tool directly to the side of the tool post "on center", chucked a small diamond burr in the tool, and used it for a rotary boring bar to enlarge the neck. Worked like a champ but you'd have laughed your butt off at how makeshift it was. I'd say it was "redneck" but no duct tape was involved, just a Big Lots plastic bar clamp from a set my wife bought me for Christmas one year.
 
#9
I have been using a dermal tool with the screwed into an aluminum tool holder purchased a number of years ago. Then it cost less than $20. I am on my second dermal tool. It is not a heavy duty outfit but for the monies involved it is one of the better investments I have made. Perfect for taking the last .001 from a punch or grinding and polishing the inlets on die bushings. The front of a dermal will screw off and screws into the holders the threads are some kind of custom threads I believe.
 

KeithB

Well-Known Member
#10
I've been ragged about my initials since James Bond movies came out.

A few extra tools, home built or commercial, can really make a lathe a versatile piece of equipment. I remember thinking when I bought my collet chuck that if it wasn't concentric I would use this tool post grinder setup and the compound on the lathe to bore the taper true. Luckily I didn't need to but it would have worked. Most hardened steels need to be machined with abrasives.
 

KeithB

Well-Known Member
#11
I love my dremel tool. I used it to cut locks off when the wife and I owned a mini storage facility. I used a 12 VDC to 120 VAC adapter that would plug into my cigarette lighter socket. I would just pull up next to a unit and open the truck window and cut off the lock, took two or three minutes max. I use a pneumatic pencil type grinder in the shop instead of the dremel, I have an air compressor and I think the air powered grinders are a little more durable for what we do. But I love my dremel where I have electricity and no air.
 

KeithB

Well-Known Member
#13
FWIW - I just checked the threads on my dremel tool and by golly it IS a bastard size thread. It's a 3/4-9. Standard UN coarse is 3/4-10.

Ian you and Brad and several other people here need to pull the trigger and get a mill. Cry once, enjoy a long time.
 

Brad

Administrator
Staff member
#14
May have some funds coming this fall for a mill.
Deciding on what I need for “size” in a mill vs what the extra $ will buy in tooling.
Always a trade off.
 

smokeywolf

Well-Known Member
#15
The only reason the scale is in the picture is to cover up some company information on the drawing.
Now Keith, you know you're not allowed to "scale the drawing".;)

I acquired a toolpost grinder about 7 years ago, but before that, I had thought about trying to mount my Dumore die grinder to the toolpost.

Is a tool grinder or surface grinder in your future?
 

smokeywolf

Well-Known Member
#17
Used to grind "drill-mill" diameters with a spin-index fixture on the surface grinders. Never had or even used a good tool/cutter grinder. I think I do have one of the low end Darex drill shapener units stored away somewhere in my shop. Used to admire the high end tool/cutter grinders that they showed off at the Westec shows.

Would be a treat to someday see pictures of your new building/shop when it's complete.
 

Bret4207

Well-Known Member
#18
I've cobbed to together a tool post grinder with a Dremel before for my little Atlas. I've even used a 4.5" angle grinder for hogging off material in the lathe, if you can call anything you do in a 6" Atlas "hogging". Used the same Dremel set up in my Atlas shaper as a sort of surface grinder. Even used a radial arm saw as a crude surface grinder once. . Necessity, mothers, invention, etc.