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View Full Version : Help me buy a tool post grinder



Theiskell
12-09-2012, 11:17 PM
I am looking to buy a tool post grinder. I have a grizzly g4003g 12-36 lathe. The problem I am having is what size to buy. I get conflicting information. One set of specs says the 44 series dumore is for up to a 7” swing and another says it will work up to a 14” swing. The 5 series looks like it will work but more conflicting info. Can someone help clear this up? I would like to get the right one the first time.

Thanks,

macona
12-10-2012, 12:29 AM
Do you really need one? What do you plan on doing with it?

J Tiers
12-10-2012, 12:35 AM
I go with the 14" camp on that. I have a 44, used to have the very smallest one, used both on my 10" Logan until I wised up and quit doing that.

The smallest one was too small, the 44 seemed a little large on the 10".

Now I just don't do it at all...... yes you can get a good finish, and yes you can take off just a fractional hair of material where needed.... But I found that the mess was not worth it. Too much cleaning up, too much covering up, and the alternative, not covering nor cleaning, is even worse.

I banished the grinders to a far corner, through 2 doors from the lathe, and 1 from other machines. The 44 is now doing duty as a T&C grinder head. And it works pretty well as that.

So I might suggest (not knowing what you want, and totally ignoring your stated intent to get one) that you NOT pay several hundred or more $$ to get the privilege of cleaning up grit from the lathe, and covering up the ways before grinding.......

Judicious use of strips of closed coat abrasive paper will do nearly all you want, with the exception of grinding the points of centers

lakeside53
12-10-2012, 01:31 AM
I have a 44-??? It was big (but usable) on my 10 inch Emco, now about right on a 14x40. Clean up isn't as bad as some may suggest; you don't have to be a clean freak for the few times a years you'll use it. Oiled covers work. A strong vac with collector at the wheel gets 90% easily. The rest takes a few minutes.

And... sand/emery paper is just as bad - you'll likely use that much more often than a TP grinder. I can have a perfect shaft bearing fit with Emery strips way quicker than I can set up the Dumore. Internal fits or long sliding fits? That an entirely different issue and the TP grinder excels.

As to the 7" or 14" issue.... probably Country based definition - some define a lathe swing as "radius", some as diameter...

Fasttrack
12-10-2012, 02:16 AM
I get conflicting information. One set of specs says the 44 series dumore is for up to a 7” swing and another says it will work up to a 14” swing.

Thanks,

I think the conflict has to do with where you are getting your specifications. There are two different standards when specifying the capacity of lathe. One standard measures the maximum distance between center of the spindle to the ways (or carriage or compound) and cites that number as the maximum swing. This is the radius of the largest work piece the lathe can handle. Other manufacturers cite this number as a diameter, so what is a "7 inch lathe" to one manufacturer is actually a "14 inch" lathe to another one. IIRC, European lathes typically cite the maximum radius while American machines tend to cite the diameter. The modern lathes all seem to cite diameter.

Ian B
12-10-2012, 03:54 AM
The common objection to toolpost grinders on lathes is the grit problem. This obviously comes from the grinding wheel, not the work (lathes get covered in all grades of metal swarf anyway). Never having done it, but how about using a type of grinding wheel with negligible wear characteristics? I'm thinking of a CBN or diamond wheel. These work fine on t&c grinders, why not in a toolpost grinder?

Ian

Jaakko Fagerlund
12-10-2012, 04:04 AM
+1 for vacuum dust extractor. People tend to get too anal about grinding on the lathe, especially when people use emery almost every time and don't clean afterwards as thoroughly.

One chinese lathe I know has been used for the past 18-20 years, no repairs on the ways and it still hasn't had any major wear on the ways. This is a 40+ hours per week machine, mainly mold components and bearing work, so emery do get used a lot and often. The machine still makes straight turning and isn't worn out at all.

So yeah, just clean up like you always do as a maintenance and you'll be fine.

tdmidget
12-10-2012, 04:18 AM
The common objection to toolpost grinders on lathes is the grit problem. This obviously comes from the grinding wheel, not the work (lathes get covered in all grades of metal swarf anyway). Never having done it, but how about using a type of grinding wheel with negligible wear characteristics? I'm thinking of a CBN or diamond wheel. These work fine on t&c grinders, why not in a toolpost grinder?

Ian
Negliglible wear characteristics? No such thing. The basic principle of grinding is that new edges are exposed by deterioration of the wheel. A tool post grinder has absolutely no more accuracy than the lathe. It uses the same ways and lead screws. You can get the same finish with abrasive paper or cloth. It is good for materials such as rubber that do not cut well with edged tools.
The grit problem? Are you under the impression that diamond (not for use on steel) or CBN will not harm your ways?

Ian B
12-10-2012, 05:05 AM
td,

Have a look at http://books.google.nl/books?id=TSLfCwmzwdQC&pg=PA10&lpg=PA10&dq=wear+rate+aluminium+oxide+vs+cbn&source=bl&ots=lCHM1ZDFdj&sig=qCEQs76rXOp0IvbhYX8dEItKeQM&hl=en&sa=X&ei=NqzFUPiTFvCU0QWW5oGwCQ&redir_esc=y#v=onepage&q=wear%20rate%20aluminium%20oxide%20vs%20cbn&f=false

It shows wear rates of CBN to be in the region of 1,000 to 2,000 times less than with aluminium oxide. Relative to aluminium oxide, that seems negligible to me.

Considering that a toolpost grinder spends far more time in it's box than on the lathe, and that it'll most likely get used for the very occasional finishing grind on a hardened component, my point was that the amount of abrasive grit that it'll put on the lathe's ways will be small. I'm guessing that the OP is a hobbyist, and doesn't keep his machinery in an air conditioned room with a filtered air supply. His lathe will probably suffer more from corrosion, airborne dust, particles from the occasional use of an angle grinder or bench grinder elsewhere in the shop etc than it ever will from a toolpost grinder. Reducing the amount of abrasive from grinding can only be to the good.

You can indeed get the same finish from abrasive cloth. What abrasive cloth doesn't do, however, is restore the original roundness or straightness after a part's been machined and then hardened. The OP didn't say what he wanted a toolpost grinder for, but this would be the use that I'd have for one.

Ian

Toolguy
12-10-2012, 05:37 AM
I use my Dumore 44 on a 12 x 40 lathe once in a while. It's a good size for that and works well.

J Tiers
12-10-2012, 08:15 AM
Basic covering and a vacuum system should work better than covering alone. But it is surprising how the grit travels. I find it a hassle to use the TPG, and agree that abrasive paper strips are a lot easier to deal with.

As for abrasive paper "throwing grit", closed coat paper releases much less, and it isn't "thrown" as with a wheel. Plus, one generally uses the paper with some oil, or at least I do for finer grades, so the issue of "throwing grit" is almost non-existent.

Jaakko Fagerlund
12-10-2012, 08:59 AM
diamond (not for use on steel)
Use one first and then come to talk.

Ian B
12-10-2012, 09:15 AM
Use one first and then come to talk.

Yes, I seem to remember that John S has some opinions on that one...

Ian

Theiskell
12-10-2012, 12:36 PM
As you can see from the picture I am pretty anal about keeping things clean. To answer the question what do I want it for….I have had several occasions where it would have been nice to have precision grind on a motor shaft. I know that there are other ways to get a nice finish but what’s the fun in using sand paper when you can use a cool tool. I am pretty through about cleaning after using any type of abrasive so I don’t think I have a problem there. I would also like to grind a nice three jaw chuck that is a bit out. I’m sure it won’t get used much, but it would still be nice to have it when I need it.
Thanks for the help on the size. It sound like a 44 series is the way to go.
A question for those of you that do use one; what application do you use it the most for? External or internal grinding. To me it would really shine, grinding a bore on something.


http://i224.photobucket.com/albums/dd295/theiskell/IMG_4864.jpg

Jaakko Fagerlund
12-10-2012, 12:48 PM
Yes, I seem to remember that John S has some opinions on that one...

Ian
Yep, and it is not a long time ago when I 'destroyed' 25 mm dimater 100 mm long steel rod in to pulver with a diamond coated wheel. And this was to test if I could destroy that said diamond coating, but had no indication whatsoever to even scratch it.

rohart
12-10-2012, 06:22 PM
I had several dead centres that had seen better days. I also had a toolpost drill. And I had just finished a Quorn T&C grinder (but the head was not remobveable as per the spec.)

So I made an adapter to allow me to use the several grinding wheels on arbors I had prepared for the Quorn in my TP drill.

I covered the ways and had at my dead centres. The result was little short of fabulous. I was almost sorry I didn't have any more to do. I will certainly look forward to the next toolpost grinding I have to do.

The finish was superb. When turning with carbide or HSS I find I cannot guarantee a good finish, whether I haven't sharpened the finishing tool, or I get too close to the finished dimensions before going for the sharpened tool. Grinding, the finish was perfect every pass. Slow, needing some clean up, but perfect.

The only downside was I was feeding the topslide by hand for the 60 degrees, but that's hardly the fault of the process.

Gunsmithing
12-11-2012, 01:43 AM
I use a Dumore 44 on a 9" South Bend for over 30 years work great

Dave

oldtiffie
12-11-2012, 02:18 AM
If nothing else, a tool post grinder is very good at grinding material that is too hard for the lathe.

It does give a very good class of finish.

It is no more or less than another cutting tool in the lathe tool-post. It is a pseudo cylindrical grinder.

I doubt that lathe "size" or "swing" is a real consideration at all - just use common sense.

J Tiers
12-11-2012, 08:45 AM
I doubt that lathe "size" or "swing" is a real consideration at all - just use common sense.

it is really only in three ways.....

1) the power of the grinder vs the size of work to be fitted onto the lathe. Small grinders and big work don't go together well for getting things done reasonably fast

2) The ability of the support means of the grinder (a post and clamp for those) to get the wheel to center height

3) The 'stickout" and wheel size as it relates to grinding reduced diameters on the size of work that fits the lathe. The 44 has a 3" normal wheel size. the smallest one has a 2" wheel size

oldtiffie
12-11-2012, 05:12 PM
I agree JT.

Its just that some people get real (too?) excited and anal when TPG's and "air quills" get an airing.

If a small grinder on a big job on a big lathe seems to be oncongrous - but will eventally do the job (and is the only thing in the shop that will) then short of not havig the job done then by definition that (too?) small TPG is the best if only tool for the job.