# Toolpost grinder questions



## Brian Rupnow (Mar 11, 2013)

I am considering buying a toolpost grinder for my lathe from Little Machine Shop.
http://littlemachineshop.com/products/product_view.php?ProductID=2001&category=
I simply don't have the ability to turn small precision parts like needle valves for miniature carburetors on my 10" x 18" lathe. Once I get below about 3/32" diameter stock, the material just flexes away from even my sharpest HSS tooling. I am assuming that with a toolpost grinder like the one shown in the picture and link, that I could grind these small items to the required taper. I would be using this for unhardened mild cold rolled steel. I would also use it to grind the sealing faces on miniature valves like the ones on the small i.c. engines I build. I don't know the first thing about toolpost grinders, but for $150 I am willing to learn, especially if I can use one to make these small parts that I have no other good way of making. The one in the picture is 2" from the center of the grinding wheel to the base, and they suggest removing the compound rest and bolting it directly to the cross slide table. My lathe measures about 3" from the center of the chuck to the top of the cross slide table, so I realize I would have to machine an adapter plate. Of course, this would leave me with no way to set up angles to grind tapers, so I would probably have to have an adapter plate with drilled and tapped holes at whatever angles I would most commonly wish to grind on tapered needle valves. Any insight that you can give me in respect to what i want to do would be much appreciated.-----Brian


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## cfellows (Mar 11, 2013)

I've not had good a experience with toolpost grinders.  I had a small Dumore grinder and could never get a very good finish with it.  Don't know if I was using the wrong grade, grit, or composition, but after trying a number of different wheels and speeds, I decided it must be a black art that I didn't want to invest any more time in.  

That's just my experience.  I'm sure others will have a different experience.

Chuck


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## chipenter (Mar 12, 2013)

I would be looking to turn the mounting through ninety degrees , and mount it on the tool post for tapers , as I have only 2 3/16 " over my saddle .


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## Brian Rupnow (Mar 12, 2013)

It would be much simpler if the grinder could be held in one of the tool holders on my AXA quickchange toolpost. Does anybody know of a company that sells a set up like that?


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## canadianhorsepower (Mar 12, 2013)

Brian Rupnow said:


> It would be much simpler if the grinder could be held in one of the tool holders on my AXA quickchange toolpost. Does anybody know of a company that sells a set up like that?


 

Hi Brian 
I did build one like this for both my Taig lathe and my Craftex ct o89 
I use this attachement specialy to do carb adjusting screw when changing
a motor from gas to alcky. The only thing I change is the base attachement
to my quickchange and my top plate is adjustable.
I'm sure youll figure it out
cheers

http://www.deansphotographica.com/machining/projects/filingrest/filingrest.html


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## n4zou (Mar 12, 2013)

Brian Rupnow said:


> It would be much simpler if the grinder could be held in one of the tool holders on my AXA quickchange toolpost. Does anybody know of a company that sells a set up like that?



You can do a quick and dirty mount with a peace of key stock that will fit in a tool holder, hose clamps, and a die grinder.


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## n4zou (Mar 12, 2013)

cfellows said:


> I've not had good a experience with toolpost grinders.  I had a small Dumore grinder and could never get a very good finish with it.  Don't know if I was using the wrong grade, grit, or composition, but after trying a number of different wheels and speeds, I decided it must be a black art that I didn't want to invest any more time in.
> 
> That's just my experience.  I'm sure others will have a different experience.
> 
> Chuck


The trick is using water soluble cutting and grinding fluid such as Monroe Astro-grind A


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## MachineTom (Mar 12, 2013)

Having used a few different TP grinders over the years there are things that add or subtract from success. First is rigidty, the more rigid the better, this will show in the surface finish right away, waves, scallops, lines,  mean lack of stiffness. IMO mounting a TP grinder as pictured to a QCTP is asking for poor results. Mount a TP grinder to the compound, if that type can't be modified to do that  don't buy it. Something not often considered is the lenght of the spindle from wheel to belt, a center in the TS is often needed on long work, but then the spindle hits the TS base, I doubt your mini lathe has the crosslide travel to clear the TS and twist the grinder to clear, and still contact the work. 

If your lathe does not have reverse, you need a grinder that can be reversed, the wheel has to turn opposite the work, which means in forward the sparks from the grinder go UP. The wheel speed needs to be 5-7000 sfpm to work well, thats 15k rpm on a 2" wheel.

Having both a diamond and a boron stick dresser are necessary to get the best finish on the work. Each time you mount the grinder to the lathe it will be on a different angle to the lathe travel, the wheel needs to be dressed so the grinding face is dead nuts parallel to the travel of the carriage or compound or your finish will look like a poor threading job. When taking a deep cut which is a cut .002-4" you narrow the face of the wheel, because you have so little power to turn the wheel from these small motors. So on a 1/4 wide wheel should be an 1/8 to 5/32 wide in contact. Since you don't have the wheel spindle running parallel to the work, you only dress the corner this wide. For a finish cut of less than .001 you can widen the dress to 1/4 if the motor can handle it.

When dressing the wheel the type of dressing holder that can clamp to the work, or a chuck jaw is the best to get the face square to the work.

The speed of the work should be around 100 sfpm but is not critical, just in that range is good.

I currently have a Themac TP grinder 1/3 hp, and this is great on a 12" lathe, I had a Dumore before this and used it on the Myford S-7 quite a bit. It was a  little 1/14hp with a 2" wheel, but did a great job just slowly. For a mini lathe that would be the ticket. 

You could take the 150 for the LMS unit and add an equal amount, then buy a used Dumore, and be happy. IMHO


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## Brian Rupnow (Mar 12, 2013)

Maybe for the small amount of grinding I want to do, this is what I want. My shop has an air supply. this one fits in the boring bar holder on an AXA toolpost. It sure looks a lot handier, but I suppose a great deal would depend on what type and grade of "mounted points" (grinding wheels potted onto arbors) are available. it would certainly be better than having to unbolt the compound rest and all of the nonsense involved with the first grinder I showed. It would also be angle adjustable and could be fed at an angle. Remember, this is only for needle valves and perhaps very small (as in 3/8" diameter) valves vor i.c. engines.


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## loggerhogger (Mar 12, 2013)

One thing that i have had good success with when turning small diameter thigs like needle valves is to spin the shaft in your chuck, and use a hand file to form the tapered point. You can also use this method to reduce the diameter of small shafts without having to worry aboutthe tool digging in because of flexing.


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## canadianhorsepower (Mar 12, 2013)

loggerhogger said:


> One thing that i have had good success with when turning small diameter thigs like needle valves is to spin the shaft in your chuck, and use a hand file to form the tapered point. You can also use this method to reduce the diameter of small shafts without having to worry aboutthe tool digging in because of flexing.


 

check post #5 that's exactly what your talking about they work awsome


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