Surface Grinders

How risky is it to buy a used surface grinder? What should I check for? Would I be better off buying a new Chinese import rather than a used, older American made unit?

Did you do any homework? Enter "buying surface grinder" in the search all forums and you will have a few days worth of reading, most of it repetitive, on what to look for in a surface grinder. This question comes up every other week.

Here's a couple recent ones to get you started.

http://www.practicalmachinist.com/vb/showthread.php?t=149417&highlight=buying+surface+grinder

http://www.practicalmachinist.com/vb/showthread.php?t=144240&highlight=buying+surface+grinder

short answer: an awful lot of used surface grinders are not near as good as the sellers believe them to be. But surface grinders in general are pretty cheap these days. So if you can inspect one, you may find a deal. If you buy a new chinese surface grinder, you should still be able to inspect it.

5 block test is a paliative for suckers. Useful if you own the machine to determine if chuck needs reground. Nearly useless to tell if the ways are any good unless they are so bad the table hops up and down at every reversal. Indicating the chuck is useless. A wallered out chuck fresh ground on a wallered out machine will still read "0 - 0" everywhere with the indicator on the wheelhead of the machine. Offsetting the indicatorsignificantly to either side might give some clues, but is not really informative about over all condition.

However, depending on the nature of your work, a grinder with perfect ways that will grind a full length piece flat within a couple tenths, might not be necessary. A grinder in fair shape with some wear may still grind small pieces and tools to tolerances difficult to measure with conventional equipment. If that is the case (mostly small work in comparison to the machine size work envelope) a $250 618 grinder in nice shape ("pretty good" ways) with ugly paint might be better value than a perfect one for many thousands more. Worst case is buying a new "looking" one for many thousands that actually grinds like a worn out one with clapped out ways. But you have to be able to inspect it reliably to make the determination.

If you intend to do regular surface grinding, as opposed to mostly small tool making & sharpening, get one with auto feeds at least in X & Z. (Z is spindle axis, table in out, which is not Y as some mistakenly have it)

Beyond the ways, the spindle should be good. You can listen, or grind some samples after dressing the wheel. But there is a fairly long learning curve on doing nice looking grinding on a range of substrates; and the choice of wheel type/grit/hardness/style of dressing makes sometimes make a big difference in results. So a bad first effort might not automatically condemn the machine. Might mean you have some more experimenting to do.

my long short list of reccommendations and pet peeves on the subject of surface grinder purchase

smt

Well checking for banana ways and bad spindle would be a start.

I'm thinking if you have a long accurate parallel, you could lay it on the chuck (magnet off) and indicate across it and also look underneath it.

I've been pondering this myself since I'd love to have a 6x18 manual.

Clutch

clutch said:

I'm thinking if you have a long accurate parallel, you could lay it on the chuck (magnet off) and indicate across it and also look underneath it.

I've been pondering this myself since I'd love to have a 6x18 manual.

Clutch

Click to expand...

Sounds like a good idea, Clutch. Where would one go about purchasing a long accurate parallel such as you are describing? My guess would be that it would need to be scraped and made of cast iron.

Stephen Thomas: I need to be able to hold .0001 for 12" for the tooling I'm making.

Is that flat within .0001, on size to .0001, parallel to within .0001? In any event, that is a tall order. That could be a tough order for a good grinder hand, and near impossible for a newbie grinder hand, even if he is an excellent Bridgeport machinist.

The Chinese stuff I know of is out. You should be looking for the best of the American, Japanese, or European equipment.

If I were in your shoes and had to meet a tolerance of .0001 of about any type on a surface grinder, I would spend the long dollar and buy a machine that the dealer was willing to "run off" to prove capabilities. Make sure you have all the necessary test equipment to inspect the finished parts to better than .000025, and take it there for the run off.

Your project will not be for the faint of pocketbook.

Quote: "Stephen Thomas: I need to be able to hold .0001 for 12" for the tooling I'm making."

Just as an exercise for information purposes, lets say the part is a smidgeon over 4" wide so we can call the diagonal 13"

Acccording to Starrett, the spec for a Grade A (laboratory grade) inspection plate is:
(40 + diagonal squared/25) x .000001" (unilateral) x 2

(40 + 13^2/25) x .000002 = .0001+

Suggestion is that part will be better than Lab grade surface plate.

That's a flatness spec.
As Gbent notes, you are not clear on what you want to hold to .0001"

It's a daunting proposition.
smt

gbent said:

Is that flat within .0001, on size to .0001, parallel to within .0001? In any event, that is a tall order. That could be a tough order for a good grinder hand, and near impossible for a newbie grinder hand, even if he is an excellent Bridgeport machinist.

The Chinese stuff I know of is out. You should be looking for the best of the American, Japanese, or European equipment.

Click to expand...

Flat within .0001. Parallel within .0001.

Holding those tolerances is no mean achievment, I think you'd be well advised to look at a new machine and a good quality one at that. Regards Tyrone

math error:
I woke up realizing that when posting the equation (spec.) for surface plate flatness above, i mentally multiplied 13^2 & came up with 269, or 100 too much. Can only say "It was late at night!" This really does not change things much, though.

The flatness for a grade A surface plate is as posted, (40 + diagonal squared/25) x .000001" (unilateral) x 2

So for our 13" on the diagonal hypothetical example,
(40 + 13^2/25) x .000002 = .000094 or a bit under .0001; not ".0001+" as posted above.

Also, the spec does not really consider plates under 12" x 12" square.

Minor math error notwithstanding, the OP requires to surface grind parts flat to much better spec than shop grade (grade B) surface plates, and within a few millionths of Grade A spec.

Good grinders will indicate within that range on good inspection procedure. Producing parts to that spec will involve rigidly controlled process and a bit of "art" as well. Temperature effects, both in the work (induced) and in the machine as it warms or cools. Table "float" depending on current operating cycle of the machine. Removal or addition of stress in the parts. etc, etc.
I'm not familiar with it, but think you are getting into lapping territory to make any rapid headway with parts. I scrape to get better than .0005 or so on large parts, and then am at the limit of the accuracy of my surface plates.


What material are you grinding, and what is the width & thickness?

smt

stephen thomas said:

What material are you grinding, and what is the width & thickness?

smt

Click to expand...

Material is A2. Width varies. Thickness is .125, .25 and .5 Do you have a source for a scraped 18" cast iron parallel for use in checking a surface grinder? If I have small quantities how hard would it be to lap in say .0002 by hand? What materials and tools would you recommend for lapping?

like steve said ...
buy an 'orable one and you may be suprised.

and you may end up with one as good as mine

grinds an 8 x2x1/2 to within two microns

0.000078 Inch im not worthy of it !!!!

how it looked



after pressure wahing ....which took all the paint off ...was found a gem underneath.



all the best.markj

With head mounted Diaform and automatic down feed as well. Don't suppose it's got a silver lady on the front of the bonnet has it?

The only thing that mine's got to compete with, is that it's a 1400 and it cost me £75.

I'm not really insanely jealous, just a bit

aboard_epsilon said:

like steve said ...
buy an 'orable one and you may be suprised.

Click to expand...

I would be very surprised to find an honorable used machinery dealer or reseller. I prefer the trust but verify approach. Been burned too many times.

Quote: Do you have a source for a scraped 18" cast iron parallel for use in checking a surface grinder?

Just google "granite surface plate" or "granite parallels"

here are some examples. I have bought Starrett products (trustone). Have no dealings with any of the others, listed only as examples, not reccommendations.

http://www.tru-stone.com/pages/smp.asp#acc
http://www.granitemeasuring.com/G_parallels.htm
http://www.1gg.com/html/pargranite.html

I'm not finding finished CI straight edges, seems Newman has discontinued them, but does stock the composite Al/CI face type. Imagine they would be somewhat temperature sensitive. http://www.newmantools.com/busch/a6100.htm

Challenge may have discontinued CI as wel, but they sell granite Straight edges and parallels http://www.challengeprecision.com/mall/Granite Plates and Blocks/Granite Straight Edges.htm

Anyway, google is your friend.

You don't need a true parallel, only one side flat, and shims. Or use a small (12 x 18) surface plate and shim it on the table. For any of the above, keep in mind the spec limits of the gage if you need higher limits for your product.

Here's a brief description of inspection by G & L, and a table of tolerances for their rebuilt grinders: http://www.barkermill.com/Saddle.htm

Our own Milacron has had a nice ELB for sale for a while. Maybe he'd cut a deal, since you don't need the creep feed feature http://www.procyonmachine.com/cgi/disp_prod.pl?pg=prod&item=29 Also a lapping machine, but probably too small for your needs: http://www.procyonmachine.com/cgi/disp_prod.pl?pg=prod&item=36358

Quote: "If I have small quantities how hard would it be to lap in say .0002 by hand? What materials and tools would you recommend for lapping?"

As mentioned, I am not really familiar with lapping.

smt

Two things , pressure washer !!!!! It's a machine tool, I don't even use a pressure washer on my car Nooooooooo Waaaaaaaaay. You're lucky it stayed on that pallet truck. Regards Tyrone