Surface Grinder???

[precisionworks]

I don't know how many others on CPF have this machine tool, but it's something that sees a lot of use in my shop. Bought mine used from Machine Tool Ted, who continues to get into my pocket, even this week It wasn't expensive as American iron goes, seems like $350 or $400 IIRC.


This grinder belongs to a member of the Yahoo Group, but is a dead ringer for mine ... although mine is normally covered in a film of oil & grinding dust.

Surface grinders are designated by the size of the table X&Y travels. For the Toolmaker, that's 6" x 12", usually written 6x12 (roughly 150 mm x 300 mm). There is also movement in the Z (vertical) axis, as the head can be cranked up or down the column for coarse adjustments, plus a fine adjustment calibrated in .0005" ... which is easy to split if you need to remove just .00025". On this machine, the head can also be rotated for angled grinding or special work.

Here's a photo of the one in my shop:

More info here: http://www.metalworking.com/Dropbox/DeltaToolGrinderCatlg1-4-pdf.pdf

Ask any questions you want, and I'll post some photos showing different set ups if anyone would like to see those.

 

[wquiles]

I don't have one, and have not needed one yet, but I am certainly intrigued and would like to learn more :devil:

How wide is the path being grinded? About 1/2" (width of the wheel, right)?

Will

 

[precisionworks]

How wide is the path

It can be as wide as the wheel, which is 1/2" on the Toolmaker. Normally, the wheel is started just off to one side of the part, advanced .050" toward the part, and the first pass is made. Then the table is moved another .050", another pass is made, etc. until the entire surface is ground.

The reason that it's done this way is that, even after truing the wheel with a diamond point, the wheel still has minute high and low spots. By advancing the part just a fraction of an inch at a time, only a very small wheel contact does all the grinding ... looks like no more than 1/8" in width on most parts.

This photo shows parallels that have been run under the wheel:

An interesting rebuild article here: http://benchtest.com/

 

[modamag]

It's a really cool toy for handling tenths. For flashaholic however, I don't see much use since most of what we deal with is circular.

 

[precisionworks]

I don't see much use since most of what we deal with is circular.

+1

Other than grinding shims for customers, the SG is mostly used to repair things that used to be flat - fixed parallels, adjustable parallels, mag bases for indicators, etc. It's also the tool for building fixtures or jigs where the fixture has to have a dimension (or dimensions) accurate to .0005.

If you're making a run of parts, where all parts need to be the same height, you can mic each one, which is awfully slow. Or you can set up a stack of gage blocks & use a height gage, which is many times faster. But if the job is one you do on a regular basis, it makes sense to grind a custom gage block, mark the dimension on the side, and pull it out each time it's needed.

Same thing applies to setting a sine plate, which is an ultra precision angle plate.

If you look closely at the bottom of the photo above, you can just see the stack of gage blocks that are used to set the angle. If the angle is 'special', a custom ground gage block is worth making for repeat use.

In most shops, the SG is a tool for working on tools

 

[FredM]

Is this what they use to resurface heads and engine blocks?

 

[StrikerDown]

Is this what they use to resurface heads and engine blocks?

Those are usually done on a mill.

 

[65535]

I was going to say, they don't seem practical for a lot of DIY projects unless you work with precision parts. I can see though for a machinist it would be a invaluable tool. I suppose if you pony up for a toolroom lathe and a mill you might as well fork over a few benjamins.

 

[LukeA]

I've always wanted one. It'll get parts about as close to perfectly flat as you can get them.

 

[PhotonFanatic]

So, to Jonathan's point--what's good for circular items? A toolpost grinder, I suppose, but that leaves who knows what all over your lathe.

Your suggestions, please.

 

[modamag]

If you're making a run of parts, where all parts need to be the same height, you can mic each one, which is awfully slow. Or you can set up a stack of gage blocks & use a height gage, which is many times faster. But if the job is one you do on a regular basis, it makes sense to grind a custom gage block, mark the dimension on the side, and pull it out each time it's needed.

Barry, I always learn something from reading your posts here and on PM. You know I bought a sine bar for almost 3 yrs but yet to use it "once". Maybe one of these days.

 

[wquiles]

Barry, I always learn something from reading your posts here and on PM. You know I bought a sine bar for almost 3 yrs but yet to use it "once". Maybe one of these days.

+1

I have learned lots already - and look forward to learning more from Barry

Will

 

[precisionworks]

what's good for circular items? A toolpost grinder

That is THE tool for OD or ID grinding. There must be a hundred posts on ways to make a TP grinder, with the most simple being a fixture that mounts a Dremel to the cross slide. Next up is a small motor driving a belt that spins a cartridge bearing spindle. Or a commercial unit like a Dumore:

Some of the shop built units are pretty cool, the ones from CNC Cookbook.com being as neat as I've seen (one uses a Porter Cable router motor to generate the high spindle speed needed for small diameter stones, the other is based on a DeWalt Zip Tool):

http://www.thewarfields.com/cnccookbook/MTLatheTPGrinder.htm

that leaves who knows what all over your lathe.

A lot of people are overly concerned about grinding dust & abrasive grit destroying their lathe. If you're careless, it can, but a few simple precautions allow grinding on the lathe without compromising the machine.

Cover exposed ways with a cloth, or an oil soaked paper towel. Run a shop vac nozzle as close as possible to the grinding wheel contact. If the carriage needs to be advanced or withdrawn while grinding, spray the ways heavily with WD-40 which carries the dust down to the chip pan. Clean up really well after grinding (again, WD-40 will remove 99% of the grit on the ways & cross slide). Remove all chuck jaws, spray it out with (you guessed it) WD-40, relube with your preferred chuck oil, and reassemble.

Lathes are pretty tough machines. A small amount of TP grinding, with a thorough clean up, isn't going to harm one. If you plan to TP grind 8 hours every day, you'll want a dedicated machine for just this purpose.

 

[will]

The shop that I worked in had a small surface grinder. We would turn it on, clean the wheel with a diamond point, and grind down the item. We did not turn it off until the part was finished. For the most part, the items we made were tool jigs to make other items. It was not really a production grinder. We were a prototype shop, we made a lot of individual jigs for jobs. For the home shop, there are probably a lot of other tools that would see more use.

 

[precisionworks]

turn it on, clean the wheel with a diamond point, and grind down the item. We did not turn it off until the part was finished.

On smaller machines, without an automatic wheel dresser, that's the method most often seen. If the wheel gets clogged with metal fines and has to be redressed, you have to reestablish the Z axis zero point, remeasure the thickness of the part, and continue working to the final thickness dimension.

Big, production, CNC machines have an automatic wheel dresser built in. After X many passes over a part, the wheel is lifted, dressed, and touches back down - in less time than it takes to describe what's happening. Since all the motions are controlled by ultra high precision ball screws & digital sensors, the machine "knows" exactly how much the dresser removed and adjusts the wheel position to compensate for that.

CNC grinders aren't the only machine that does that - many VMC's and HMC's (vertical or horizontal machining centers) have tool wear compensation built into the program. After a particular insert has been run a few times on a certain job, it isn't hard to calculate how much wear occurs per minute at the cutting edge (usually expressed to the sixth decimal place, or millionths of an inch). That constant is plugged into the program, and the machine automatically moves the insert closer to the part as the tip wears down - keeping each part at the same final dimension as the part that was made six or eight hours earlier.

 

[65535]

PW, assuming you mostly work with nonferrous extra tough materials would it be advisable to use a high quality diamond wheel on those? Once worn in I would imagine the diamond wheel wouldn't have appreciable wear over the life. My thought on that though is anything short of about 60RC would probably clog up the wheel pretty quick and ruin it. Maybe for precision carbide grinding?

 

[precisionworks]

nonferrous extra tough materials

Do you have specific materials in mind, as well as the exact alloy of that material?

 

[65535]

Not specifically, I was imagining cobalt steel, tungsten, hardened tool steels, hardened stainless steels. Maybe even titanium.

It didn't seem like a practical idea for anything that would load up a grinding wheel, and most materials load up diamond wheels.

Also I'm curious, can TPG really produce closer tolerances on parts. I can imagine for large parts (12"+) but for most machining Ops, around 6" would it really be better than a final pass with a proper finishing tool. (Or insert).

 

[precisionworks]

Knoop Hardness (Hk)is a good way to judge what material may be used to cut another material.

Hardened Steels run from 700-1300 Hk. Aluminum oxide wheels run 2000-3000 Hk, so they'll easily cut hardened steels. The general rule is to select aluminum oxide wheels for surface grinding or TP grinding of steels, stainless steels, annealed malleable iron & tough bronzes. Silicon carbide (2100-3000 Hk) is used for grey iron, chilled iron, brass, soft bronze, aluminum, and cemented carbides.

can TPG really produce closer tolerances

It does produce a better surface finish, and it's a lot easier to hit an exact ID or OD. Most machinists, when doing a bearing fit that needs to be within +/- .00015 (which is a target that's only .0003 wide) will turn the part .001 oversize, and file to final dimension. A carbide insert, no matter how fresh & sharp, pushes against the work with great force in order to peel or shear material from the surface. The TP grinding wheel needs very little force (by comparison) to remove material. And the aluminum oxide wheel is harder than carbide, with sharp grains, which allows fine control. Hitting .0001 or less is easy with a TP grinder, and the finish is spectacular.

If the dimension isn't really critical, or the surface finish doesn't need to be super fine, conventional turning is faster & less costly when time is figured in.

 

[65535]

Ok so for flashlights SF and TPG is rather useless for the actually machining. BUT as far as a machinists standpoint it's invaluable on precision work.