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Dumore 44 tool post grinder questions

techymechy

Aluminum
Joined
Oct 24, 2018
I'm a newby and am just starting a shop.

I bought an older Dumore 44 tool post grinder that hasn't been used for years. I turned the spindle and motor by hand and things seemed to turn fine. The motor has the #4 sheave on it and the spindle has the #3 sheave on it (supposed to be 15,000 rpm spindle speed). I bought some Velocite #6 oil and put 20 drops in the spindle and spun it by hand for a few minutes then places the belt on the motor and spindle and turned it for a couple of minutes. I then added 6 more drops of oil and ran it for maybe 10 minutes. Then I added 6 more drops and ran it for 10 minutes. then I added about 15 more drops and ran it for 10 minutes and measured the bearing temperatures. The instructions say not to add more than about 50 drops at one time.

My garage temperature is about 66F. The max bearing temperature on the belt side was about 112F (Trise ~46F). The max bearing temperature on the grinding wheel side was about 130F (Trise ~ 64F). I have zero experience with these grinders. Is my bearing temperature too high or what is too high of a temperature?

I look forward to your thoughts?

The spindle did turn easier after oiling and running.

Dave
 
The temperature's not excessive, but there's other things to worry about with a grinder, including spindle stiffness (how much it wobbles between wheel and housing), and axial play (does it move along the axis of the spindle).

You also need to worry about wheel balance (especially with larger wheels) and other losses of stiffness in the lathe (compound and cross slide slop, as well as headstock stiffness).

What do you intend on doing with the grinder? If you're a newb, do you have a plan for the work you want to do, or are you accumulating tools as they become available?
 
Howdy,

Thanks for the reply.

I am a newb and am I'm setting up a hobby shop for retirement. I am getting tools when they come available and are reasonably priced.

The spindle has no perceptible play either axially nor radially on both ends. I didn't run a dial indicator on it, but it definitely has no play by feel. I have the stone dressing tool with the grinder and probably 4-5 stones. I reckon a good wheel should balance out with the dressing tool, right? I haven't rang the stones that I have yet nor followed the directions in the manual to check for cracks, etc. I have read that one should only expect to take off about .001" on diameter (max) with each pass of the grinder. Given the stiffness of my lathe, I think that this is about right. I'm just starting to run the grinder and insuring that the spindle and motor are OK before trying to grind anything.

I have a little 9" logan lathe as my main lathe. I purchased an identical lathe that was in parts. My idea was to set up a second lathe just for tool post grinding near my other grinders - sort of a poor mans cylindrical grinder and share the accessories between the two lathes. I have a larger sheave on my lathe jack shaft and will run this in the slowest sheave in back gear. That should get my grinder lathe spindle speed below about 50 rpm (but I have to measure it for sure). I'd basically seal the grinder lathe as good as possible from the grinder grit and just leave it be.

I'd like to finish punches and dies with the grinder. I have been case hardening some punches and dies and thought it would be fun to grind them back to size. The punches and dies grow a little when case hardened. I've been accounting for this size change by machining the offset before case hardening. I've been getting pretty good surface finish with a light/slow feed final pass with a sharp tool and then polishing with 500 grit wet/dry but thought I could get better by using a finish grind. Also, I just want to learn how to grind. I think my case should be about .040" and I can easily hit dimension on the grinder w/ this amount of case.

Dave
 
With smaller wheels it's less of an issue, but due to how wheels are made simply truing them does not confirm balance - there can be varying density within a wheel.

Do crack check every wheel before use, having one blow up is no fun. Ditto confirm wheel speed capacity, you don't want to run a wheel faster than its rated speed. When in doubt, discard a wheel. Your safety should override trying to save a few bucks.

As to the overall plan of using the grinder - give it a go, be cautious (wear eye protection!) and ask questions here. There's people with much more grinding experience than I have, but they're typically using more "professional" setups and machines, so keep that in mind.
 
Tool post grinders wreck lathes. A lathe also makes a fairly crappy grinder if you've ever used an actual grinder to compare. Best thing to do is put it away until you really need it, which hopefully will be never. You also need to consider if you can even get the thing on the centerline of the Logan. They don't have much distance between the compound and part axis. I have a larger Dumore and can't get close to center on my Logan 211.

If it's old, you might want to rebuild the spindle to be sure the bearing preload is correct and working right. Given oil lube, I think the temperature is a bit high.
 
Ya, I agree, it's always best to be careful than run a cracked wheel that comes apart at 15000 RPM. I actually had one come apart on a Dremel tool and I wasn't wearing eye protection. Luckily, nothing happened except to scare the heck out of me and super reinforce the need for eye protection. Haven't worked on the lathe or other rotating tool since w/o eye protection.

I will dedicate one of my Logan 400's for the grinder. It is a lathe that I'm putting together with a bunch of parts. I don't think I have enough pieces to make the carriage drive so I'll have to do that by hand. Like I said, I'll do my best to seal everything up on the lathe and then leave it alone with the tool post grinder mounted. The 44 was designed for a lathe this size. I have to admit, I don't have the lathe together nor the grinder mounted, but that is the project I'll tackle after getting new mill set up. I know that tool post grinders are not the best grinder, but it's a way to get this functionality in space constrained shop.

For the tool post grinder, how does one check the bearing preload? What should the temperature be or how does one determine what "good" is besides using the grinder and checking surface quality?

Conrad - thank you for the reply. I would also like to thank you for your web site. I have used your information on the Eico 666/667 extensively. I'm also into restoration of antique radios and electronic test equipment.

Dave
 
Listed wheel RPM should be thought about to avoid a wheel blow-up. Good to stand out of the line of fire staring a wheel or starting a grind if you can and ring ringable wheels.
If the has no end play when dead cold and sounds and grinds well then preload is likely ok. Below too hot to hold is good. Preload might be fine for 3000 RPM and run hot at 20.000 so good to pay attention if making a big speed change.
 
I think my dual ID/OD spindle is rated for something like 45,000 RPM, a totally insane speed for the lube setup, which is none. They greased it. I rebuilt it with new bearings and oil, with the intention of pulling the end and reoiling when necessary. What I'll probably do is grease it with a high Dn Kluber grease and not run at maximum speed. The reason I think your temp is high is because mine doesn't get that hot running near twice the speed with oil. I don't know how they built yours, but mine is preloaded with Belleville washers. It's really important for the bearings to be able to slide in the housing with that method, otherwise the preload is a complete unknown. I had to make up some custom pin wrenches to service it, but it was really pretty easy. New bearings from Dumore are fairly expensive. I went with ORS bearings from Turkey and they're really very good and far less expensive. My only other critical comment on these things is the motors howl like crazy. Ear protection is a must. Maybe the 44 isn't as bad as my 57, which sounds like a living room full of vacuum cleaners.
 








 
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