Toolpost (or other) grinding in the lathe

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

petertha

Well-Known Member
HMEM Supporting Member
Joined
Jun 24, 2010
Messages
2,362
Reaction score
932
I thought it might be beneficial to share information & experiences on this subject because it seems to come up often. The typical reason behind grinding in general is to achieve a high degree of accuracy as well as surface finish. Personally, I am interested in what you have achieved with classic 'lathe based' TPG (tool post grinders) like Dumore, Themac or maybe other brands out there. Specifically any example projects, metals, what kinds of abrasives, speeds, feeds, measurement controls.... Or maybe you built a custom accessory for grinding specialized work – bearing shafts, crankshaft journals, cylinder liners or other engine/tooling gadgets.

(I hope this link comes across) but this is one of my favorite posts of some of Jim Allen’s prior model engine work.
.90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine

2 popular commercial TPGs
Themac Themac | Tool Post Grinders | Lathe Grinders
Dumore Tools - Dumore Corp

I’ll kick things off with my own (very limited) experience on the TPG front & some random pictures. Maybe like others I initially cobbled a Dremel type tool in a holder. If the parts were tiny, at best one could say they came out shiny as long as the magic smoke stayed in the motor. But dimensional accuracy was….hit & miss. What was I expecting with $10 bearings sitting in a plastic housing? Something approaching a die grinder was a bit better, but not really. Most suffered by lack of clamping rigidity IMO. I pondered some offshore integrated motor/spindles, some with handy ER collet shaft ends & variable speed typically used on homebrew cnc routers. But generally low-ish watts and/or rpm, seemed a bit more like a speculation buy & looking more & more like a 'real' grinder.

I hummed & hawed about building my own spindle. And soon recognized I knew little about specialized bearings, temperature compensation, specific spindle oils, motors or VFD’s, requisite lightweight belts to achieve low vibration shaft speeds between say 10-40K rpm, … Eventually I decided to get a Themac J35 when the $ opportunity presented. On the plus side it seems like high quality spindle, longstanding industry history, USA manufacture, variable spindle height positioning to suit different lathe swings, a range of OD & ID accessories, relatively easy mount to lathe compound with T-plate adapter.

On the negative side - cost! I suspect commensurate with what is involved to manufacture them. Although there are some used deals out there. The Themac also has kind of an oddball proprietary shank taper that inserts into the spindle cartridge & must be an accurate fit. Eventually I figured out dimensions & made a few arbors of my own. Grinding wheels of specific size & grit & abrasive are not exactly common either, at east in my part of the world.

The bigger rub with TPG’s in general (and maybe this is more my own naivety) is they don’t seem to play well with applications where work is supported by a tailstock (TS) center. The TPG spindle wants to be pretty much exactly where the TS is. And I would think TS support represents many if not the majority of typical precision grinding applications. One can extend the TS quill to full length which helps by presenting the smaller OD, but not really enough & also loss of support. Theoretically you could mount a large diameter wheel which would bring the spindle back out of the way of TS. But I run out of table extension if towards operator. One could mount the TPG at an angle & dress the wheel at an angle, but now you might be limited in terms of approaching a raised boss on the shaft & certainly couldn’t grind in between a small gap like crankshaft journals between neighboring counterweights. I had this idea to mount the TPG on my cross slide on the opposite slide to give more room & would also help stabilize the motor base. But most TPGs I’ve seen seem to be 3-4” max wheel dictated by fixed motor rpm + pulley arrangement.

So without this sounding too much like buyers remorse, just wondering if anyone else has some uplifting applications to share?
 
Last edited:
First off - wheels. I found a few references to making your own. I was a little concerned about shooting my eye out, but my initial applications were ID grinding so maybe safer if it failed inside the part. So I bought a 1/4" wheel, came up with a drawing that swiss cheesed a bunch of profiles & had a water jet guy cut them. Quite accurate, about the same dressing effort. Offers a wide(er) range of grits & composition.

So far so good, no accidents. Now I find myself looking at my regular offshore Dremel stones with being held with a blob of epoxy on a piece of steel shaft, hmm.....
 

Attachments

  • IMG_5539_edited-1.jpg
    IMG_5539_edited-1.jpg
    35.6 KB · Views: 378
  • IMG_2823_edited-1.jpg
    IMG_2823_edited-1.jpg
    196.4 KB · Views: 392
  • IMG_2824_edited-1.jpg
    IMG_2824_edited-1.jpg
    210.7 KB · Views: 357
  • IMG_2825_edited-1.jpg
    IMG_2825_edited-1.jpg
    224.5 KB · Views: 365
  • IMG_2826_edited-1.jpg
    IMG_2826_edited-1.jpg
    158.4 KB · Views: 382
Last edited:
Here are some of the Themac arbors & show the tapered section I was referring to. I'll post some custom arbors I made but reverse engineering the taper angle was kind of a pita. I don't have a taper attachment in my lathe which made matters worse. Eventually I got the taper recipie so it blued as good or better than the stock arbors. And heads up, the thread DP doesn't precisely match the typical class threads so the mantra is 'just replicate it'.
 

Attachments

  • 7-3-2016 0004.jpg
    7-3-2016 0004.jpg
    21.5 KB · Views: 316
  • IMG_3384_edited-1.jpg
    IMG_3384_edited-1.jpg
    300.3 KB · Views: 323
Here is what I would call an example of a typical TPG mount up in the compound & successful grind - cylinder liner IDs. I've tweaked some improvements since these pics were taken, more to follow.
 

Attachments

  • IMG_0730_edited-1.jpg
    IMG_0730_edited-1.jpg
    42.4 KB · Views: 449
  • IMG_2635_edited-1.jpg
    IMG_2635_edited-1.jpg
    83.8 KB · Views: 460
  • IMG_2636_edited-1.jpg
    IMG_2636_edited-1.jpg
    92 KB · Views: 438
I made this wheel dressing tool which clamps to the lathe bed. Goes without saying the ways are wiped of oil, covered, vacuum in position to immediately suck the abrasive dust.
 

Attachments

  • IMG_2643_edited-1.jpg
    IMG_2643_edited-1.jpg
    105.7 KB · Views: 357
  • IMG_2645_edited-1.jpg
    IMG_2645_edited-1.jpg
    203.6 KB · Views: 365
  • IMG_5703_edited-1.jpg
    IMG_5703_edited-1.jpg
    32.9 KB · Views: 377
  • IMG_5704_edited-1.jpg
    IMG_5704_edited-1.jpg
    27.3 KB · Views: 355
I found the biggest challenge was measurement of intended vs actual material removal. My DRO is 0.0005" resolution which is actually kind of coarse for most grinding applications. I was hoping to target say 0.0002" diameter resolution with some confidence & even that was leaving myself 1-2 thou final lapping allowance. The somewhat disturbing factor is once the TPG motor is on, it kind of makes micro vibrations accross the cross slide & the dials get 'lively'. My lathe lead screw / backlash / gib adjustment is in nice shape and I think the TPG motor assembly is well balanced. But it does impart a buzz to the machine.

When I lock the cross slide it stays put, but it became apparent early in the game I needed some better more absolute measurement. It took a couple iterations & everyone's machine is different but this what I came up with. A clamp that holds a 1.5" dial tenths reading indicator via T-slot mount. And a simple aluminum block with epoxied magnets to act as a plunger reference stop. I can reverse things around or screw in an extension rod to accommodate most setups. I got in the habit of stopping the TPG motor, make the DOC adjustment when everything was quiet, then take another pass. Reversing power feeding out of an ID bore was generally not a good thing. probably a function of my '98 vintage Taiwan lathe.

In reality grinding to a target is kind of a juggling act. The wheel might be wearing, it may require several spring passes to spark out. It has to stay cool or at least same temperature. I didn't mess around with coolant or air too much but I also wasn't removing much material thus far.
 

Attachments

  • IMG_3392_edited-1.jpg
    IMG_3392_edited-1.jpg
    141 KB · Views: 307
  • IMG_3393_edited-1.jpg
    IMG_3393_edited-1.jpg
    147.8 KB · Views: 318
  • IMG_3394_edited-1.jpg
    IMG_3394_edited-1.jpg
    183.8 KB · Views: 319
Last edited:
Here is my recent idea of mounting TPG to the opposite of the spindle more or less directly on the cross slide. To my mind it eliminates a few extra sliding sources involved with the compound mount, kind of the wedding cake stack-up syndrome. Shows the normal mounting plate with hold-down nut. I would just bolt the motor to a new larger solid plate with c/s flathead bolts & then secure the plate via T-nuts. That part is straightforward, makes a nice line to the lathe spindle center.

Mostly I was hoping for some tailstock clearance solutions to arise if I used a larger wheel, but it seems to be a dead end in that regard. I'll try to take a better pic of the tailstock conflict but hopefully you get the idea.
 

Attachments

  • IMG_3323_edited-1.jpg
    IMG_3323_edited-1.jpg
    420.3 KB · Views: 409
  • IMG_3325_edited-1.jpg
    IMG_3325_edited-1.jpg
    165.1 KB · Views: 421
  • IMG_3330_edited-1.jpg
    IMG_3330_edited-1.jpg
    209.2 KB · Views: 393
  • IMG_3331_edited-1.jpg
    IMG_3331_edited-1.jpg
    204 KB · Views: 406
  • IMG_3332_edited-1.jpg
    IMG_3332_edited-1.jpg
    227.7 KB · Views: 408
It's most interesting but it has been covered here and elsewhere - literally Donkkey's Years ago.

Nevertheless, it certainly has has a place.

Somewhere else here there is a mention of several workers and Ian Bradley who also write as Duplex with Norman Hallows published a design in his book "the Grinding Machine'. Again, the excellent and quite revolutionary New Zealander -- Jack Radford also published a design in his book. Mention regularly appears here of the Quorn tool and cutter grinder and the 'cartridge' can be removed and used in the lathe. So, in similar vein are the ones in the Stent and Kennet tool and cutter grinders.
More modestly, years ago, I bought a wood router from Robert Bosch of Switzerland and found that it actually came from a tool and cutter grinder with a 1/4" /6mm collets. So with a standard 43mm collar, I made up a holder to put it on my - now gone Myford Super7B.
I still have it and a new-er Myford Super7B with power cross feed.

So I look forward to further articles

Thanks

Norman
 
Heres one I knocked up using an unwanted (at the time) cheap 6" bench grinder, shown here finishing the main bearings of an R&B gas engine, Please note, this was a first try and the grinder does have a guard fitted now.
RB Gas Engine 245.JPG
 
I know this is a bit crude but it did the job but the method could be used for occasional grinding.
 
Maybe some kind of shielding for the lathe ways was added after the pics presented.
If not - - - - would suggest doing so any time any kind of grinding is done on a lathe.
The spent grit is still a grit and it truly plays hob with lathe ways. Its also a real pita to clean off of and out of all the nooks and crannies!
As I was told of surface grinders - - - - they grind themselves to death.
 
Maybe some kind of shielding for the lathe ways was added after the pics presented.
If not - - - - would suggest doing so any time any kind of grinding is done on a lathe.
The spent grit is still a grit and it truly plays hob with lathe ways. Its also a real pita to clean off of and out of all the nooks and crannies!
As I was told of surface grinders - - - - they grind themselves to death.
Totally agree, Just out of shot in my picture is a whopping great Magnetron magnet directly under the cut and in the coolant flow. It sticks nicely to the bedway and collects pretty much all of the grinding dust.
 
Here is my recent idea of mounting TPG to the opposite of the spindle more or less directly on the cross slide...

Thank you for your detailed description and photos of the project. THEMAC was located in my hometown until the last acquisition, still in the same area. Goldstar appropriately notes that there is hardly anything new, except rediscovery of old solutions. :)
 
Lofty76, that is a nice solution. Just to confirm, are you able to traverse the entire length of stock & the motor clears the tailstock in that setup shown? Is the grinding wheel itself 6" diameter or you just mean nominal grinder size? Do you recall offhand what the motor diameter is? Did you do any upgrades to the bearngs or used as-is? I have a 1/3hp slim motor light duty bench grinder but guessing its still 5" diameter.

The nice part about spindles is they are slim by comparison & motor can be displaced out of the way via a belt. The Themac spindle is ~ 1.5-2" diameter. But the downside is making an appropriate arbor for a big wheel & probably too high of rpm using kit pulleys. Sourcing an appropriate motor may be the easier problem to solve as long as the rpm matches or could otherwise be controlled.
 

Attachments

  • 10-2-2020 12-16-11 PM.jpg
    10-2-2020 12-16-11 PM.jpg
    91 KB · Views: 274
Just to add my experience -



This was my first time of using my Quorn spindle on the lathe and it went well although I somewhat resented all the time it took both to do the grinding and the very long clean up time required to remove all the damaging dust. If I was charging my time then buying new rotors would have been preferential but as a hobbyist we don't mind substituting time for money! It took me 3 years to build the Quorn and all the fitments required to sharpen difficult tools but I have never regretted the investment.
 
Found this video by Don Bailey (of Suburban Tool fame) showing an OD grinder in action. Now that looks like the weapon of choice! Now that I see (large) wheel / motor / tail stock layout of the 'real' machine it rather confirms something more like what Lofty76 has accomplished. The ODG is a pretty robust piece of kit as one would expect. The entire bed/table pivots too, which explains how tapers are are ground & replicated consistently.

 
Specifically dedicated to model engine cam shafts using what look like harvested Sherline components. But kind of similar layout recipe - a bigger diameter wheel to grind a relatively small part between centers & circumventing the tailstock. Hey, maybe a repurposed Chinese mini lathe + bench grinder dedicated to this grinding task c/w coolant & keep the mess completely off the 'good' lathe LOL.

http://modelenginenews.org/techniques/camgrind.html
 

Attachments

  • SNAG-10-2-2020 0000.jpg
    SNAG-10-2-2020 0000.jpg
    103.6 KB · Views: 468
Lofty76, that is a nice solution. Just to confirm, are you able to traverse the entire length of stock & the motor clears the tailstock in that setup shown? Is the grinding wheel itself 6" diameter or you just mean nominal grinder size? Do you recall offhand what the motor diameter is? Did you do any upgrades to the bearngs or used as-is? I have a 1/3hp slim motor light duty bench grinder but guessing its still 5" diameter.

The nice part about spindles is they are slim by comparison & motor can be displaced out of the way via a belt. The Themac spindle is ~ 1.5-2" diameter. But the downside is making an appropriate arbor for a big wheel & probably too high of rpm using kit pulleys. Sourcing an appropriate motor may be the easier problem to solve as long as the rpm matches or could otherwise be controlled.

Hi Petertha, The motor is 3.5" diameter and only 150 watts, but in the photo is rotating an 8"x 1/4" wheel. Had to use that size wheel in order to clear the crank webs. On stripping the original grinder down, the bearings were found to be SKF and I didn't consider they needed changing as the motor runs virtually silently. The base was originally plastic and replaced by a T6 aluminium version, milled from a solid bar. The only problem I had was with cooling, the motor was not vented and got hot quite quickly, the solution for this was to drill a series of 3/8" holes equidistant around each bearing housing end and a fan fitted to the spare wheel spindle end to provide a flow of air. The motor can now work for over an hour without getting more than slightly warm to the touch. However, with such a small motor the cuts have to be very delicate but overall I am extremely pleased with the finish.
 

Latest posts

Back
Top