(Dumore copy) tool post grinder
Click here to go to the Dumore web site to fault find your poor grinding job
Flea markets are a great place to wander around and kill a morning. When I saw a 1960's industrial grade tool post grinder with accessories, in a wooden case, for the princely sum of $100 AUS I jumped at it - an absolute bargain.
For the money I got an Australian made Waldown unit - very similar to the American Dumore of the same vintage.
It came with a motley assortment of vintage cup and valve grinding/refacing stones, an additional quill with long tapered spindle for internal grinding and buffing (often missing from these kits), a full set of unused internal grind stones, and a spare drive belt.
The unit hadn't been resprayed or doctored up, and was in original as used condition.
It turned out to be the "C0" model.
Seen mounted on my
10 x 18
below. This sized lathe is really too small to achieve correct
centre line alignment when mounted on the topslide (where it should be).
When new, this grinder must have cost a considerable sum.
The motor spins at 12,000 RPM and the spindle speed can be geared up or down using various diameter pulleys as required.
The 1/2" tool post mounting hole was not designed for Chinese engineering, so the 10mm bolt and stepped flange on my top slide presented a problem.
I machined up an adapter plate, but it was not ideal, as the centre line axis was about 10 mm higher than the lathe.
I used it like this until I had time to correct the issue. The options were to heavily machine the grinder mount (which I didn't want to do) or to make up a specific mount for the cross slide (which I did).
While I was at it, I incorporated it into a "super" toolpost and overcame some topslide flex issues at the same time.
So the grinder mount is actually the base of a heavy duty toolpost. You can see details of this here.
The downside is that you need the topslide to grind sharp tapers (eg. centres), so the heavy base, while good for most jobs, has it's limitations.
Below are two shots of the new mount before I polished out the machine marks from the fly cutter. Using the toolpost grinder for the same job, those marks would be non existant as there is no shock loading from the cutter. A great machine.
This "super" toolpost is also super rigid.
Fine adjustments can still be done using the micro adjuster on the carriage stop.
Other photos on this page show the grinder mounted on the original spacer (which got the unit up and running quickly).
Left side below.
And the right side - showing the two speed pulley on the motor. The larger pulley is only used for the internal quill, which requires extreme rotation speeds for the very small stones.
The grinder mounts rigidly, and is a solid and well made unit.Close examination revealed the spindle bearings in both quills were bone dry, and one bearing was shot. CBC Australia Pty Ltd sourced replacement bearings for me - NSK EN12. These are a type of magneto bearing.
Here's a photo of it with the internal quill mounted, to centre my external chuck jaws.
The shaft for the internal quill was also in back to front.
When repacking and fitting the bearings I noticed what appeared to be an oil port in the top of each quill. Not being sure if the bearings ran in grease or an oil bath, I Emailed Brobo Waldown (Aust) Pty Ltd for clarification.
I was pleasantly surprised to receive a user manual for Waldown Tool Post grinders through the post - gratis. What a great company. Thank you Brobo Waldown.
The manual revealed that the bearings are greased at assembly, then oil is then added daily through the oil port for long term lubrication. The oil bath cuts drag, and lowers the temperature of the bearings enormously.
The screw head for the oil port can be seen below near the centre of the internal quill.
The dual pin wrench is used to preload the bearing retainers to remove endplay. Tension the grind stone end adjuster with the unit running until revs start to drop, then back it off to full speed, and leave it there. If necessary pack the bearing to position with paper shims.
The wrench was missing from the kit, so I made one.
I cleaned and greased the motor armature bearings while I was at it. The brushes and commutator looked quite OK. I also blew the accumulated dirt and grindings out of the field windings and motor body so that everything was as good as new.
The basic manual provides information on items including safety, maintenance, gearing ratios, grinding speeds, part numbers, and stone sizes. It's very good.
The safe surface speed of a bonded grind stone is approximately 32 metres/second.
For an 80mm diameter abrasive, that equates to a quill speed of about 7000 RPM. In comparison, a 19 mm diameter internal abrasive requires a quill speed of about 24000 RPM.
These grinders were made for industry and are the only way that very hard metals such as high carbon, case hardened, and quality high speed steel can be successfully machined.
They are a fantastic accessory, able to do a wide range of tasks. I can only begin to describe how good these units are.
Not only are they extremely accurate, but they leave minimal machining marks. Finished surfaces are excellent.
Want to slice off some piston rings without machine marks? No problem using an 0.8 mm wide friction disc below.
The grinder is used regularly. It does stuff you just couldn't hope to match any other way.
The next page gives some more information on using it.