Surface grinding on a vertical mill?

I think there are a host of reasons why you cannot use a mill to surface grind.

The table feed strikes me as the biggest issue, although there are others that come to mind that would prevent the mill from being used. I don't think I've ever used a knee mill that was free of vibration to the degree required for a good surface finish.

I'm sure you can get a surface grinder cheap if you look in the right place. That or farm the work out.

Regards,

Robin

Of necessity, I've used my Bridgeport sans the right angle attachment (using a cup wheel) to grind with reasonable success, and recently. I do not recommend it, not at all. The addition of the right angle drive will do nothing positive in an attempt to grind, and is likely to ad certain problems to the attempt. There are certain issues associated with grinding on a mill, not the least of which is the potential for ruining the machine. Assuming you're willing to risk that, and willing to spend roughly an hour fully masking the machine, here is what you can expect:

You will not be able to achieve a decent finish, especially on light duty machines like a Bridgeport, or clone. Robin already addressed that issue, and he's right. It will be a better finish than you would expect with other tools, fly cutters being excepted in some cases.

You will be unable to take much of a cut with the wheel because you don't have the ability to traverse quickly like a surface grinder does. You can't move wheels slowly over surfaces and expect them to behave. The localized heating creates monumental problems, especially if you try grinding stainless.

You will be unable to cool your work with coolant, so that fact, coupled with the slow table traverse speed, restricts you to VERY light passes. A thou tends to be too much when grinding a narrow surface, like the planer blades I sharpened recently. A large surface would be impossible, or nearly so.

Now that you've been advised that it won't work, you're likely to try anyway. When you do, DO NOT diamond dress your wheel if you use a cup type. The large area in contact with the part raises temperatures way too quickly. A hand dress with a dressing stick and an angle on the outside edge of the (grinding) surface will yield the coolest cutting surface possible. Due to the fact that it spins parallel to the part, it will still yield a reasonable surface finish, unlike a straight (type 1) wheel, which runs at right angles to the part. They must be diamond dressed in order to leave a decent finish. They also cut very hot when so dressed.

Use an aluminum oxide wheel for all steels, and silicon carbide for cast iron and all non-ferrous and non-metallic objects, especially ceramics. Diamond in that instance would be far better.

Good luck, and check out a used surface grinder for long term happiness and successful grinding.

Harold

The one negative is that replacing spindle bearings on grinders can be very expensive. On the other hand, unless the bearings are trashed, even rough bearings would likely serve one far better than a mill as a grinder.

Harold

I can sell you a KO Lee 6" x 12" surface grinder with mag chuck, fully operational, for less then you can buy a new B'port right angle head. It's in SoCal. While we are on the subject of surface grinders I brought another KO Lee 6" x 12" last week. Mid-'80s machine with 99% of the original paint intact. This machine has coolant, hydralic powerfeed, over wheel dresser,all requisit tooling and manuals. If someone wants it before Dec. 1st, I'll sell it for $2500. Leigh at MarMachine

Gosh, you guys are incredible. There is a LOT of value in being able to tap into this "bunch of experienced guys sitting around the pickle barrel" for advice. After evereyone dinged this idea, it's obvious to me why its a bad idea. Now if I can only get to the point where these things are obvious before I ask them........

Thanks again everybody!

And Gunner, where are your grinders located? Somewhere near San Diego if I remember?

And Catruckman, where are you guys located? SoCal can be a big area to someone coming from Phoenix (where I am).

-jim

Bakersfield.

Leigh is about 150 miles south of me in Newport Beach/Costa Mesa.

Visit him on a Friday when he is open, and then run up on Saturday to see me.

Perhaps Marty E may have some stuff to go this way, or that way and could help pay your gas. I think he is interested in some of my Stuff. We have done business before.

Gunner

"I mean, when's the last time you heard of a college where the Young Republicans staged a "Sit In" to close down the Humanities building? On the flip side, how many sit in's were staged to close the ROTC building back in the '60's? Liberals stage protests, do civil disobedience, etc. Conservatives talk politely and try to work out a solution to problems through discourse until they believe that talking won't work... they they go home and open the gun cabinets. Pray things never get to the point where the conservatives decide that "civil disobedience" is the next step, because that's a very short route to "voting from the rooftops" Jeffrey Swartz, Misc.Survivalism

Gunner, I might be interested in one of those grinders. I'm a knifemaker in Santa Barbara County, about three-four hours from you.

This would be for my home shop. I've got 240v but no 3-phase.

-Frank

Hmm ... *which* "Phase a Matic"? They make so-called "static" convertors, and rotary convertors.

The static ones only provide power during spinup, and then you are left with the motor running on single phase. This has two potential problems:

A rotary converter, however, should be quite satisfactory, though I would be more tempted to go for a VFD, so I could tune the motor speed to adjust for loss of diameter (and thus SFM) as the wheel wears.

And it is a *lot* cheaper to make a rotary converter from an old three-phase motor of about 50% more horsepower than the load motor. (you could even use the "static" converter as a starter on this kind of converter.)

Enjoy, DoN.

Thanks, Gunner. I'm still considering it. Looking for a phase converter that won't cost more than the grinder, plus I got to run it by the woman who wears the pants in the family.

-Frank

A rotary phase converter is pretty easy to build. I built one for about $200, including a used 3 HP idler, new start cap and connection hardware from Grainger, and a pair of run caps from SurplusCenter.com. My design was based heavily on

A lot of people on rcm have built RPCs, and there is a lot of good information available by searching the newsgroup with google. Search for Fitch Williams, Bob Swinney (also wrote an article in one of the Village Press magazines - either Home Shop Machinist or Machinist's Workshop), Jim Rozen, Don Foreman, etc.

Pete

VFDs are now cheaper that rotary phase converters. When I bought my grinder, I asked here about using using a VFD vs a rotary phase converter and the general opinion is that the VFD is better than a RFC.

After experimenting a bit with a static phase converter and running multiple 3ph motor I believe that a motor running on a rotary phase converter is pretty much running on 2 legs (ie single phase) until the load motor is loaded enough to slow it down to the point that the idler motor is now generating some power for the third leg. This explains why some guys in the group stated their grinders gave a better finish with a VFD than with a RFC.

You can buy a 1HP VFD for less than 200 bucks. I certainly would not buy a new RPC for 500.

chuck

Where?

Teco, new in box with warrenty. I got 3 of em and I like em.

This depends on whether you have taken the time to tune the RPC. Appling capacitors of the proper size between the generated phase and both line phases can balance the output, so you get current from all three lines. (And a load factor correction capacitor added between the two lines can significantly reduce the out-of-phase current drawn from the line. If you are on a home electrical service, you don't get charged for that extra current -- but it increases the chances that the circuit breaker will trip at just the wrong time. :-)

Certainly a VFD gives the proper (synthesized and well balanced) three phase, but a tuned RPC should do almost as well. What it *won't* give you is the ability to tune the motor (and spindle) speed.

Certainly. I don't think that anyone was suggesting that you buy a *new* RPC. At least, my suggestion was that you *build* one, using a used motor and as many used components as you can get.

But I also pointed out that a VFD would be nicer, for the extra money.

One other thing to remember with a VFD -- don't place a switch between the VFD and the motor. Let your switch command the VFD to start and stop and you should be fine. Switch between the motor and the VFD and you are likely to zap the output transistors of the VFD with the switching voltage spikes. (You can get away with it anyway, if the VFD is sufficiently oversized for the load. E.G. I am using a 7-1/2 HP VFD to run a 1HP horizontal mill, and that I can switch between the motor and the VFD (and actually *must* do so, as the VFD is too far away to wire convenient remote switching.

Good Luck, DoN.

When I first installed a VFD on my grinder, I thought I would be clever and increase the motor speed so that my grinding wheel was running close to the max RPM. That translated to about 62Hz instead of 60. It seemed like the finish was not as good at 62 as it was at 60. I figured that the motor and spindle are balanced at 60 and it was best to stick with that speed. I suppose that the VFD could be used to increase speed for smaller wheels if needed though.

cs