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View Full Version : Surface grinder question, and a bit of a rant.



tdkkart
03-30-2009, 02:03 PM
Being somewhat of a newb, and not having full experience on all the machines in a well equipped shop, a question popped up this morning.

Assuming a smallish manually operated surface grinder, how does one compensate for the wear of the wheel that will ineviteably occur when grinding larger pieces, say 4" x 8".

Many people people are of the impression that a "surface ground" part to be the holy grail in flatness, yet if the piece is largish at all it would be near impossible that it would be truely flat.


So what brings this on??
Being more in need of a rudimetary hydraulic press than long on time to source the parts and build my own, I recently bought an off-shore press. A bit better than the average HF model, but a far cry from a Dake.

As usual, the press came with a "pair" of free press plates, you know, the 4x6x1 or so plates of steel with a V notch cut in one side.

I mention "pair" because these plates were laughable. A "set" maybe, but certainly not a "pair". Even the Chinese should realize that a "pair" of anything tool related, especially items that are specifically intended to be used together, at the same time, should probably be a relatively matched "pair".

I seem to have gotten a mismatched set, more like a couple, of plates.
Lenghth, width, height, and thickness were not anywhere close. The thickness was reasonably close, depending on whether you measured the high or low spots. I realize they don't need to be as close as gauge blocks, or even a pair of V-blocks, but they should be in the same neighborhood with each other.

The worst(dangerous) part was the fact that the edges had horrible angles cut by a dull flame wrench. Had these plates been stood on edge and any pressure applied they would have rolled over and shot across the shop.

So, while I was standing there watching my mill carve them down into a somewhat matched pair, I thought "these sure would look cool with a ground finish", and then realized how much work it would be on the machine that I have access to, a 6"x12" with a 1/2" wide wheel. Also realized that they probably wouldn't be flat when done.

Carld
03-30-2009, 03:00 PM
Well, for one thing as the surface grinder is doing it work it is only cutting on the edge of the wheel and it moves across the work. The rest of the wheel is just dusting off the surface. That means that you can make several passes back and forth across the work before it needs dressing and the sound of the wheel on the work will tell you to dress it plus the excess sparking.

I seldom take more than .002-.003" off the surface on each pass. If you have coolant on it you can take more. After you get the surface cleaned up the you take another pass without moving the wheel down and just dust the surface to get the surface flat.

You have to be carefull when using the mag table that you don't pull the warp out of the plate and then grind it because when you release the magnet the warp will suddenly reappear.

Carld
03-30-2009, 03:00 PM
Well, for one thing as the surface grinder is doing it work it is only cutting on the edge of the wheel and it moves across the work. The rest of the wheel is just dusting off the surface. That means that you can make several passes back and forth across the work before it needs dressing and the sound of the wheel on the work will tell you to dress it plus the excess sparking.

I seldom take more than .002-.003" off the surface on each pass. If you have coolant on it you can take more. After you get the surface cleaned up the you take another pass without moving the wheel down and just dust the surface to get the surface flat.

You have to be carefull when using the mag table that you don't pull the warp out of the plate and then grind it because when you release the magnet the warp will suddenly reappear.

Carld
03-30-2009, 03:00 PM
Well, for one thing as the surface grinder is doing it work it is only cutting on the edge of the wheel and it moves across the work. The rest of the wheel is just dusting off the surface. That means that you can make several passes back and forth across the work before it needs dressing and the sound of the wheel on the work will tell you to dress it plus the excess sparking.

I seldom take more than .002-.003" off the surface on each pass. If you have coolant on it you can take more. After you get the surface cleaned up the you take another pass without moving the wheel down and just dust the surface to get the surface flat.

You have to be carefull when using the mag table that you don't pull the warp out of the plate and then grind it because when you release the magnet the warp will suddenly reappear.

TGTool
03-30-2009, 03:04 PM
Actually, surface ground parts are quite flat if done with the usual grinding practice. After dressing the wheel, left-right traverse is started slightly longer than the length of the piece. Bring the wheel down slowly over the part, and the highest point if you can find it so it just touches. Back the table out so the wheel clears the part and lower the wheel by just a couple thousandths if you're not sure what the whole surface is like. Then start crossfeed, (continuing the left/right constant movement) and when you begin to cut on the piece move the part in toward the column about .030" for each back and forth cycle. This way you'll gradually cover the width of the part. The wheel will break down, but it will primarily just round off the front corner so as you're moving across the piece the area of the wheel behind the advancing edge will still be at the original dressed diameter. Finally, when you have the surface ground (redressing the wheel as needed) take an additional downfeed of just a half to a thousandth and cover the whole thing again with perhaps a larger crossfeed increment this time. The wheel diameter will not have broken down significantly during this last cycle and the piece will be as flat as the machine's ways can produce.

<edit> Carl beat me to it (three times). Must be my slow day.

Carld
03-30-2009, 03:07 PM
Well, for one thing this site was loading so slow I posted it three times.

wierdscience
03-30-2009, 08:30 PM
.001" is an average DOC for a surface grinder,even that requires either oil or coolant to keep the wheel from glazing.

Now,about those press plates.First thing I would do is see if those plates are even steel.A drill bit is the easiest way to determine this.If you get powder or easily crumbled up curls it's cast iron or malleable iron.At that point throw them in the scrap they will hurt you.Cast plates will bust unexpectedly in a press and turn into shrapnel.Just a heads up.

Roy Andrews
03-30-2009, 08:47 PM
i guess my first question is just how precise of work you expect to do on a hydraulic press? the plates on mine certainly are not straight any more. if you want the plates to be flat i would start out on the mill or planer. surface grinders are for finish work. as far as standing plates on their sides in a press that is a dangerous practice and i would recommend that you make up some upside down "T" to support things if you need an edge.

Roy Andrews
03-30-2009, 08:49 PM
Well, for one thing this site was loading so slow I posted it three times.


that will certainly teach it a lesson.

tdkkart
03-30-2009, 09:11 PM
Now,about those press plates.First thing I would do is see if those plates are even steel.A drill bit is the easiest way to determine this.If you get powder or easily crumbled up curls it's cast iron or malleable iron.At that point throw them in the scrap they will hurt you.Cast plates will bust unexpectedly in a press and turn into shrapnel.Just a heads up.


Most definitely steel, and seemingly pretty decent stuff that machined rather nicely. Didn't find any nasty stuff hidden just below the surface or anything like that. Am well aware of what a cast plate would do in a press.
The biggest issue was just the goofy angles on the edges, didn't actually measure the angle but had to take more than .060" off one side to square it up.

No, I don't expect to do hugely accurate work, but it would be nice to be able to setup stuff with some semblence of flatness. Having parts rocking back and forth on the press makes me a bit nervous.
The surface grinding was just an idea that popped into my head for appearance sake.

TGTool
03-30-2009, 10:06 PM
Do you actually have a surface grinder then? That would be a good way to go to level up your blocks since they could probably be done together to be assured of the same dimensions. There ought to be enough tool shops still around Cedar Rapids to have them done, or stop out at Kirkwood and see if whoever heads the machinist program now would take pity on you and straighten them up.

Mcgyver
03-30-2009, 10:50 PM
Assuming a smallish manually operated surface grinder, how does one compensate for the wear of the wheel that will ineviteably occur when grinding larger pieces, say 4" x 8".

Many people people are of the impression that a "surface ground" part to be the holy grail in flatness, yet if the piece is largish at all it would be near impossible that it would be truely flat.

.

so what is flat? there is no truly or perfectly flat, something can only be flat to a tolerance......and the smaller the tolerance, bigger the surface (especially if its thin) the more difficult it is to do.

the surface grinder is no silver bullet - really flat is difficult, especially if you're talking a 4x8" piece that is comparatively small in section, say 1/2" thick. if you are trying for surface grinding accuracy, tenths, the mag chuck itself will distort the work so when its released the work is no longer flat. How do you over come this? tediously mapping out the surface with an indicator and shimming the work until its not distorted. the other way, less perfect, is to turn the mag off for the final passes usually the residual mag power to hold the work

see the point though? the challenge isn't wheel wear, its how to hold the work so its not being distorted.

Wheel wear first off not as fast as might think, secondly if you've been doing heavy roughing you can redress before finishing.....but the way you avoid wear affecting accuracy is overlapping strokes. If you start with a fresh dressed 1/2" wheel and each stroke is advanced say .100", one side of the wheel does most of the work while the other barely makes a cut - this side will not really wear at all.

tdkkart
03-30-2009, 11:14 PM
Do you actually have a surface grinder then?

Not in my shop, but have access to a couple that I use on occasion, just never done anything of this size before. Normal stuff is maybe 2" in diameter max, run a couple sets of vise jaws, that kind of stuff.

I doubt that a 6x12" magnet will have enough umpf to warp a 1" thick plate??

dalee100
03-30-2009, 11:55 PM
I doubt that a 6x12" magnet will have enough umpf to warp a 1" thick plate??

Hi,

Wanna bet?:D I've spent many hours grinding plates for die sets to +/- .0005" corner to corner. Those chucks get a good grip, and can bend some pretty heavy thicknesses. Fortunately, most of the surface grinders I've run have vari-chucks that allow the operator to dial down the strength of the magnetic field as you spark out.

Last grinding I did was a Blanchard with a 6' diameter chuck. I was blanching ASTM 633, 3 1/2"x60"x92" plates. It was a miserable job had to keep everything to +/- .002 corner to corner. It was a bear to hit the numbers.

dalee

Astronowanabe
03-31-2009, 12:01 AM
Not in my shop, but have access to a couple that I use on occasion, just never done anything of this size before. Normal stuff is maybe 2" in diameter max, run a couple sets of vise jaws, that kind of stuff.

I doubt that a 6x12" magnet will have enough umpf to warp a 1" thick plate??

my other hobby is grinding telescope mirrors.
I can promise you everything we think of as solid is more
like jello than our intuition will tell us.

doctor demo
03-31-2009, 12:57 AM
You don't need a magnet or a grinder for warping problems, hand scrape a sufface flat, turn the piece over and scrape this surface flat. When You turn the piece over, chances are good that the first surface You scraped is not flat any longer.
Like others have said, solid is not as solid as You think.

Steve

TGTool
03-31-2009, 10:59 AM
Give the OP some useful information for Pete's sake. With an electron microscope the surface might look like the himalayas, but he's asking about spacers for his press. :(

Will a surface grinder or will it not produce 1" thick blocks that will not be problematic in use on his press? My answer is that it will, even with less than ideal technique.

dalee100
03-31-2009, 02:36 PM
Give the OP some useful information for Pete's sake. With an electron microscope the surface might look like the himalayas, but he's asking about spacers for his press. :(

Will a surface grinder or will it not produce 1" thick blocks that will not be problematic in use on his press? My answer is that it will, even with less than ideal technique.


Hi,

A 7" angle grinder will produce two pieces that are suitably matched for use in a press.:rolleyes:

dalee

Mcgyver
03-31-2009, 02:49 PM
Give the OP some useful information for Pete's sake. With an electron microscope the surface might look like the himalayas, but he's asking about spacers for his press. :(

Will a surface grinder or will it not produce 1" thick blocks that will not be problematic in use on his press? My answer is that it will, even with less than ideal technique.


he asked a bunch of questions. among other things the OP asked general surface grinding stuff:


Being somewhat of a newb, and not having full experience on all the machines in a well equipped shop, a question popped up this morning.

Assuming a smallish manually operated surface grinder, how does one compensate for the wear of the wheel that will ineviteably occur when grinding larger pieces, say 4" x 8".

Many people people are of the impression that a "surface ground" part to be the holy grail in flatness, yet if the piece is largish at all it would be near impossible that it would be truely flat.

so why so critical? These questions and the responses dealt with grinding and flatness....if he's learned that there's no black & white but shades of grey on what flat means and that a piece of work moves under a force, its only a question of how much, do you not consider this both useful knowledge and in context to his above quoted Q?

aboard_epsilon
03-31-2009, 03:14 PM
yup me too ..bought this a week ago

http://img.photobucket.com/albums/v190/aboard_epsilon/Press/press6.jpg

they are flame cut ..the v's are not v's ..and there is about 1mm difference between the thicknesses .

cant complain about the price though .,

all the best.markj

Tim Clarke
03-31-2009, 08:39 PM
It's nice to have a smooth surface on press plates, for soft materials. So much easier than finding the right size/shape aluminum stock for protection.

TC

Carld
04-01-2009, 12:13 AM
The truth is he could flycut them flat and mill the sides and V's much easier than grinding them. As pointed out, they don't have to be perfect for press use.

doctor demo
04-01-2009, 12:31 AM
yup me too ..bought this a week ago

http://img.photobucket.com/albums/v190/aboard_epsilon/Press/press6.jpg

they are flame cut ..the v's are not v's ..and there is about 1mm difference between the thicknesses .

cant complain about the price though .,

all the best.markj
Mark maybe You and Tdkkart should swap one plate, it sounds like each of You have half of each others set.

Steve

chrsbrbnk
04-01-2009, 12:41 AM
I do a fair amount of surface grinding and the down feeds are more like .0002 or .0005 thou. a pass on say a 6x12 harig or okamoto even on the big 24x48's we tend to do most of it around .0002 a pass. .002 or .003 is going to really mess up a newbie even with coolant . with out coolant .003 a pass would really smoke the part. light cuts and let it cool down betweeen passses

doctor demo
04-01-2009, 01:43 AM
I do a fair amount of surface grinding and the down feeds are more like .0002 or .0005 thou. a pass on say a 6x12 harig or okamoto even on the big 24x48's we tend to do most of it around .0002 a pass. .002 or .003 is going to really mess up a newbie even with coolant . with out coolant .003 a pass would really smoke the part. light cuts and let it cool down betweeen passses
Yup, got a 13X36 Brown and Sharp and 2 tenths without coolant does a nice job , otherwise ya run the risk of things gettin hot. Even on My lil Chev with a 1/2" wheel any more than a thou. gets ugly.

Steve

Carld
04-01-2009, 09:24 AM
Maybe I'm doning something wrong but I can take up to .005" dry with my 6x12 surface grinder when roughing. It does eat the wheel fairly fast but it will last for at least 4 passes, that's four passes with the crossfeed. When I am finishing I only take .001" and then dust it with a back pass at the same setting.

It works for me even if it's wrong and I don't get a burned surface.

At one shop with a large power feed flood coolant surface grinder we always took off .010" or more when roughing.

EDIT: you wouldn't even want to hear how much rpm and down feed I used on the Blanchard grinder. You probably wouldn't believe it anyway.

Scishopguy
04-01-2009, 12:55 PM
Carl...I agree on the DOC. It depends on what is being ground and how large a surface you are dealing with. On reasonably small blocks I will rough cut at .002" to .003" per pass, while plunge grinding or grinding trace on a blank die section I will advance .005 per pass. Grinding flat stock is a little trickier, especially on large pieces. Yes, you do need to let it cool or you will get swelling and end up with a concave part.

Peter N
04-01-2009, 02:01 PM
I'll agree as well. I take 0.003" roughing cuts on my J&S 540 (6x18) and I don't use any coolant. I'll finish cut at anywhere between 0.0005" and 0.0001" on the dial, again without using any coolant.

My cross-feed is set around 0.015"-0.020" and I use a fairly fast traverse.
Never have a problem getting a good finish even in mild steel, but the harder the steel the better the finish as a rule.

Peter

pcarpenter
04-01-2009, 05:00 PM
It might be that the difference in DOC is because of a difference in technique. There was a good discussion on PM about the two methods and some of the non-believers were converts after trying a different technique:

The recommended technique was to take deeper cuts (a couple thousandths rather than a couple tenths (not huge mind you) with only maybe .010 infeed at each pass. The time lost in such tiny feed increments is made up by not having to cover the work in so many passes since several thousandths could be taken off in a single go-around.

The premise of this was as discussed already: If you feed very little at each pass, only a tiny corner of a wheel is doing the work....and changing diameter as it does it. The balance of the wheel remains the original diameter and is therefore left to handle the lots of little passes across the work before the diameter changes. The premise is that this allows for lots of coverage without re-dressing and therefore messing up your reference.

I agree though, surface grinding is overkill for press plates. It may even harden and embrittle the surface (work hardening occurs with surface grinding). I agree with the value of a good finish so as not to imprint the roughness of the surface plate on your work in some cases. However, a good flycut finish ought to be adequate I would think.

Paul

Carld
04-01-2009, 05:09 PM
Yes, and I do much as the above says and if your not using coolant then it is easy to heat and warp a part. I use a mist coolant system if needed.

huntinguy
04-01-2009, 05:28 PM
Flat is a condition of internal stress, stress induced by the wheel, sag of the part (there is actually a formula for setting blocks to measure flatness of a part), the pull of the magnet (a condition of spacing as much as strength of the magnet).

I have run .050 doc with .001 step over on mild steel with good results for roughing. I have had no success with .0005 doc with 1.0 step over. And visa-versa. It all depends on what you are doing and how good you grinder is.

Last night I was grinding cast iron and it would pull into the wheel, took forever to get it within .0005.

I have taken .02 doc by .370 wide on carbide using a cbn wheel.

There are lots of techniques for grinding, all good and all bad. Remember it is not a mill, heat is your enemy (even when you can't feel it), and nothing causes more heat faster than a dull wheel.

(May the sparks be with you)

If you want flat use half balls and double back tape. No magnetic force influence. But that does present its own set of problems.:p