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darryl
12-10-2009, 09:16 PM
I'm gonna get chewed up for this one- what's the chances of making a workable surface grinder using a belt? It would pretty much be akin to a belt sander, but with the main roller being adjustable above an x-y table and running a zirconia belt. The roller would be the point where the belt is pinched to the workpiece, unlike a belt sander where a flat area between rollers is where the belt touches down.

Offhand I can see two drawbacks- one is that a wider area of grinding surface is touching the workpiece as opposed to a wheel, which might only be an inch wide, so it might take more power- the other drawback is that the belt isn't likely to be a perfectly even thickness all throughout, so there might end up being streaks, etc in the surface being ground (or sanded I suppose).

Looks like what I'm describing is a thickness sander as made for wood, but with generally a wider workpiece than the belt- opposite to a thickness sander.


Currently I use my disc/belt sander when I want to leave a finer finish on a flat, be it wood, plastic, or metal. Just wondering if I'd get any better result using a machine such as I've described.

Bill Pace
12-10-2009, 09:36 PM
I recently sold a small 6x12 to a knife maker that had what you describe in mind to do to it. He said he knew of a couple of his knife buddies had made up, and they were bragging on them so he wanted to try one.

Might prowl the knife making sites and hit on some pics or comments on making one up --- it does sound kinda intriguing!

JoeFin
12-10-2009, 09:42 PM
I have a metalurgical machine used for preping metal samples with a very fine finish prior to harness testing very simular to what you are describing.

It has 2ea 600 grit "Wet-Belts" running over a precision ground bed with a feed pump, pumping solution directly on the belt. You simply place the sample on the belt

claudev
12-10-2009, 10:14 PM
I have seen several older factory made automotive head resurfacers based upon the use of a wide belt backed up with a machined cast iron plate. Basically just a bigger (and hopefully much more precise) version of the classic el cheapo import belt sander. The belts must have been about 18 inches wide and 8 ft long. The ones I saw had been in use for many years and still seemed to work pretty good. (Automotive heads have to be pretty flat or the engines blow a head gasket.)

A friend (and local machinist), now retired, made a version using a piece of channel and an 8 inch wide belt. He used it for many years - mainly to resurface oil field engine manifolds. He still had it the last time I looked (a few weeks ago).

Lots of ways to skin a cat.

darryl
12-10-2009, 10:44 PM
Have never skinned a cat, but have done things in many different ways :) One of the reasons I ask about this is that I have some zirconia belts begging for an application, and I could use a tool like this anyway. I'm still wondering why I can't find the 4x36 size belt in zirconia, but no matter- the ones I have are 3x24, bought as 4x36 but I never returned them. I didn't check to see if they were the right size until I went to mount one on the belt sander- uh oh, too small. Anyway it's no big deal. I probably would not want a wider one anyway for a machine like this.

I suppose I have lots of options, one being to actually buy a belt sander made for this size belt, then rebuild it into the machine I'm visualizing. Another option, and probably the better one is to build it from scratch so overall it's as solid as I want it to be.

I might as well make it do double duty. Nothing wrong with having an upright belt sander with cast iron wear plate and zirconia belt for sharpening things, plus a sliding table under the bottom roller for those kinds of surfacing operations. Hmm.

claudev
12-10-2009, 11:00 PM
Re: Zirconia sanding belts. See Enco 2009 Master catalog. Page 257. Zirconia belts from 1 x42 to 6 x 48. Quality ? Import.

knedvecki
12-11-2009, 12:11 AM
Some of the manufacturing plants that I do work at have just such a grinder as you speak of for finishing die-stamped parts usually to a tolerance of about + or - .0002 inch. They work good, other than the dust that is put into the air (that the operator breaths), which would not be there using coolant.

Evan
12-11-2009, 01:36 AM
Darryl,

Put "belt grinder" in google search and then select images. There are many possible designs from which to gain some ideas.

whitis
12-11-2009, 01:45 AM
That would be a belt surface grinder, perhaps, but wouldn't have the flatness and precision that people tend to associate with "surface grinder". You can make a machine that would work in some applications but these would be a small subset of the applications in which a surface grinder is normally employed.

There is a limited similarity to flat lapping with a sheet of sandpaper, which can produce pretty flat (but possibly tilted) results on a flat surface plate. The paper itself is fairly uniform thickness. Some issues, though. The seam of the belt, depending on how it is done, can be thicker (and less even), especially home made belts, which means that in a surface grinder like application the seam will be the low point that is doing all the work. It will work much better if the seam is thinner than the rest of the belt. Also, with any belt sander, there is a tendency for abrasive particles to abrade the platen that backs up the belt so it is curved rather than flat. Even before this wear becomes significant, they can distort the shape of the surface produced. Some belt surface grinders don't use a platen but grind against one of the rollers (in which case you want the roller to be cylindrical, not curved to keep the belt centered). Which is what you are proposing. Loose abrasive between the belt and roller still affects the surface produced. Less horsepower needed and less wear since the belt isn't sliding with respect to the drum as it would be relative to the platen. A rubber wheel would further the tendancy to produce results more smooth than flat.
http://www.centercross.com/shop/surfgrinder.htm

Another limitation is that you can't dress the belt like you can with a wheel. A wheel doesn't work well until it has been trued up by dressing on the machine it will be used on (fixing concentricity and alignment errors). You might even have to do it every time you restart the grinder due to the wheel shifting on the arbor. And when a wheel gets worn or glazed, you dress it and get more abrasive (though on some types of wheels the abrasive is a thin layer). With a belt, you run out of abrasive real fast. If your machine was rigid and precise enough, you might get flatness near the limitations of the belt itself by "dressing" the roller (before installing the belt). This would at least take out errors in concentricity and any tilt of the sanding mechanism relative to the ways. Then grind the magnetic chuck in place.

This isn't going to give a real surface grinder a run for its money. Expect results that are more smooth than flat. Which is fine for knife making but not for many of the applications a surface grinder is used for in a machine shop. May be okay for getting rid of machining marks or removing scale.

When it comes down to it, a surface grinder is a lot more than just a spinning abrasive moved over a work surface. Lots of precision ways and precisely parallel or square surfaces that need to be better than the accuracy of comparable parts on a mill. Plus precision spindle bearings. Plus rigidity. When it comes to the overall cost of doing the mechanics right, your sunk cost in those belts is insignificant so you might as well use a grinding wheel.

Sandpaper on a surface plate works because of the keep it simple stupid principle - there are no rollers, bearings, ways, frames, etc. The paper is hopefully stationary with respect to the surface plate. And you are basically replicating a precision flat surface. You lose almost all of the characteristics that make it work when you try to turn it into a surface grinder.

If you just want to use it to smooth out surface finish, you may be ok as long as the surface isn't tilted.

Turns out, this has been discussed here before:
http://bbs.homeshopmachinist.net/showthread.php?t=1922&page=2

darryl
12-11-2009, 02:30 AM
OK. I googled belt surface grinder and came up with two that fit the idea I had. Both use a fairly long belt and not very wide. If you took the lower roller off and replaced it with a grinding wheel, you'd have a normal surface grinder. At any rate, that's what I was looking to build, similarly anyway.

Thanks whitis, your discussion of that gave me what I needed to put the whole thing in perspective. I visited the link to the HSM article of some years ago, and I re-discovered the poor mans surface grinder project that I had done back then. Parts of the machine I had made are still sitting under the bench, having been robbed for parts. I think the motor and arbor are the ones that I'm using now as my toolpost grinder, though there is another motor and spindle sitting with those parts. The spindle has a tapered 'front end', with a specially made nut to hold some kind of tooling in place- wow, it's been a while- I wonder what I can use that for now hmm.

Anyway, Forrest also had some good input in that thread, and the general concensus is that a belt surface grinder could be good for smoothing flat surfaces, but wouldn't perform nearly as accurately as a real surface grinder would in terms of creating a flat surface accurate to sub thou tolerances. If I was to build the machine, it would have to be useful to me more for smoothing than anything else.

Evan
12-11-2009, 05:45 AM
Belt surface grinders are common as dirt in industry. They tend to be big, dirty and expensive to operate.

http://ixian.ca/pics7/beltgrinder.jpg

HTRN
12-12-2009, 11:13 AM
Yup. Commonly called "timesavers", after one of the companies that make them. Properly, they're "wide belt sanders". They go for big money used, and new they easy go into 5 figures.

BobWarfield
12-12-2009, 12:50 PM
Here's a little shopmade belt surface grinder:

http://www.cnccookbook.com/img/Workshop/GreatShops/KnifeSurfaceGrinder.jpg

It's from a Brazillian knife maker. See top of this page:

http://www.cnccookbook.com/CCHallOfFame2.html

Cheers,

BW