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- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] Surface Grinding Methods
- Date: Sun, 27 Dec 2015 22:28:25 -0500
http://www.practicalmachinist.com/vb/abrasive-machining/surface-grinding-methods-311562/
Thread: Surface Grinding Methods
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11-10-2015, 11:29 AM #1
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Surface Grinding Methods
I beat you to it, Michiganbuck, with the new thread.
So, the question is this: After a down feed of say, 0.001", is it a general practice by most folks to do an in or out feed at each end of the longitudinal feed? I have seen Don Bailey (Suburban Tools) do this on some of his youtube videos, and I do it quite often, mostly on non aggressive down feeds.
The issue is safety. When climbing, some have said the wheel will have more tendency to grab the work piece and send it flying, possibly blowing up the wheel in the operators face. Others have said this cannot be compared to climb milling, given the speed, diameter and other characteristics of grinding wheels, plus the fact that it is constantly being abraded, opening new cutting edges, etc.
Thanks,
Dan L -
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11-10-2015, 01:38 PM #2
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Yes. A good machine in good repair will do that with no difference in appearance. As far as safety, that's kind of up to you. It's YOUR fixturing/workholding that's at fault if the work moves.
Last edited by tdmidget; 11-10-2015 at 04:52 PM.
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Its not the wheel blowing up and killing u you need to worry about, its the heart stopping bang as things get thrown off the table!! That said, i have only done it once, now i remember to check the magnets gripped the part before starting grinding (heat treat can very much affect some steels magnetism ability!!!)
A lot of hydrulic grinders will both feed in on each pass, to a degree, climb grinding and conventional are much less different than on a mill, yeah if hogging, its a risk if it does move, but even then, normally the worst i have happen is it knocks the wheel out of true. finer finishing cuts its not a issue IME. -
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11-10-2015, 04:27 PM #4
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Thanks Dan for staring the thread. Hope more contribute because it is a good subject.
QT: [some have said the wheel will have more tendency to grab the work piece and send it flying, possibly blowing up the wheel in the operators face. Others have said this cannot be]
Mostly work on the mag or well held it will not be a problem to feed on the climb side (both sides)..* Again for most work I Infeed on both sodes of the work.
With a chancy set up coming in on the climb can change the angle of forces and loose the part.
For a super finish, fussy or get hot jobs like SS, grinding a chuck and grinding non-magnetic parts I sometimes in-feed(take more stock)on the grind side only. Tall work should be blocked in and best blocked to near the top go-side edge and for heavy grinding (Hogging) work to the go-side rail so it wont slide is an asset.
Three (of a number of) surface grinding methods are.
*Conventional grinding: One example might be: Take one down feed of .001 when you are wheel in front and off the part. Then a cross feed of (perhaps).015 each time the wheel is off the work at each end of long travel. (Your grind is .001 x .015) Yes that .001 down feed is from the zero set from the part height.
*Another method in grinding (often called plunge grinding) is to travel right and left and down feed each time the wheel is off the work. A down feed when the work is to the right side of the wheel then traveling part to the left is on the climb side. Down feeding at the right of the part(part to the left of wheel) is on the grind side.
*Form grinding is dressing a form into the wheel then most often to come down feed into the part with each down feed off part and at each right or left side(long travel) of the part with no moving the cross except perhaps .001 or so to adjust the form location. Most often with a up-feed, make adjustment, then back down.
Any one of these forms of grinding one can feed on both sides or only one side of the work.. I call them: on the grind side, on the climb side and on both sides.
Work can lay on the chuck to be parallel to the chuck. Or it can be held to an angle plate, a V block, to a fixture or to an assembly.
IMHO -
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11-10-2015, 05:30 PM #5
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Just a couple of points to add to what others here have said: I never grind without blocking around the part with parallels or 123 blocks etc. Don't rely on the magnet alone to keep a smaller pieces from moving. It's always good to have as much surface area of blocking on the magnet as possible. If the part moves on the magnet even a little, bad things will likely happen.
Originally Posted by DanLinsch
I beat you to it, Michiganbuck, with the new thread.
So, the question is this: After a down feed of say, 0.001", is it a general practice by most folks to do an in or out feed at each end of the longitudinal feed? I have seen Don Bailey (Suburban Tools) do this on some of his youtube videos, and I do it quite often, mostly on non aggressive down feeds.
The issue is safety. When climbing, some have said the wheel will have more tendency to grab the work piece and send it flying, possibly blowing up the wheel in the operators face. Others have said this cannot be compared to climb milling, given the speed, diameter and other characteristics of grinding wheels, plus the fact that it is constantly being abraded, opening new cutting edges, etc.
Thanks,
Dan L
You should consider the proper grinding of the magnet. It must be engaged and ground in using best care and minimal feeds to acquire best finish possible. Then during normal use it should be stoned prior to starting new job unless it has been in use regularly. A tiny ding on the magnet can result in work moving and bad things happening when in use.
Finally, you eluded that Don's downfeed of 0.001" was non aggressive. In my experience 0.001" downfeed was max per stroke. Until you get more familiarity with the machine and grinding processes I would stay at 0.0005". I never grind more that 0.001" on a pass and usually a couple tenths on finish if possible. Just my 2 cents.
Best Regards,
Bob -
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11-10-2015, 06:43 PM #6
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Depends on the machine. I ran a B&S 12X24 NC machine that would take .003 as easily as .001. You need a bad-ass machine and mass quantities of coolant. Technique matters. I worked with an older tool and die maker who could do it on a little Okamoto 6X18. He made it look easy but I could never duplicate his method.
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11-10-2015, 07:14 PM #7
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Your answer has a great deal to do with the grinding wheel you are using. Most don't push a wheel hard enough ( especially the semi ceramics/ cbn's) to keep it sharp. It depends on how rigid a setup, wheel type, grinder characteristics, and toolmaker's balls.....
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11-10-2015, 08:31 PM #8
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I agree if you have a beefy 10"-12" wheels you can hog some stock. However, most of my experience was using 7"-8" aluminum oxide wheels. Additionally, most our processes only used grinding for finish ops. (0.003" to 0.006" typical stock removal). I never had the chance to use Ceramics/CBN wheels but have used some diamond grit. So there are certainly alternatives. I was speaking in general regarding common 6 x 12 machines having 7" wheels.
Best Regards,
Bob -
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11-10-2015, 08:33 PM #9
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Perhaps depends on wheel, infeed and downfeed.
Don't try to creep feed grind .0.100 down and 1/2 inch wide on a form in one pass from the wrong direction.
You'll get this message fast.
Normal grinding,...50 down and 2 tenths infeed ok, 2 tenths down and 1/4 inch infeed ok. 50 down and and 1/4 inch infeed not so ok.
Bob -
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11-11-2015, 08:50 AM #10
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Another method is crush grinding. Crushing to shape the wheel. One needs a crushable wheel, that is a wheel that has a bonding that is easily influenced by harsh pressure to fracture the bonding and let loose evenly so the wheel takes the exact form of a roll crusher. One can take a roll form of serrations or the like, a lathe turner shape, even a dull cutter that is rolled against the wheel so the wheel takes the form. Then the wheel is used on the part to take the form. Often one will take the form to a roughed in wheel and the create a second roll form.. Making a second roll form for a fraction of the new roll form price. With grinding the part the profile is ground into the part. Crushable Grinding Wheels
For a one time job one might make a roll form on the lathe of CRS because that is harder than most other steels in unhardened state. A roll might be made of tool steel and brought to 48RC so it will be hard and lasting but still restored with a lathe. A roll may be made very hard so it will last for a very long time for repeat job.
Often a masking tape might be set to the side of the roll with perhaps .980 for the tough off location off the side opposite the tape for Touch to the wheel and move for dressing the wheel. Another note on the tape might be P- .747 meaning to touch the dressed side of the wheel to the part face and move that amount for grinding the part.That way the original set is restored and the part and the form should be within .001 to allow less adjusting in. -
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11-11-2015, 09:27 AM #11
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Thought we would have more guys sharing ides here..I don't want to hog the thread so help out.
The surface grinder has three lines of reference. The table being flat and true, the bump rail (rail to the far side back of the chuck should be close to zero) and the front rail (the rail in the go direction (rails should be .001 of better). With starting a part one should consider “what is the most important side” for the quality of the part. The part set to that magnetic surface and set to the appropriate rail.
The surface grinder should have a name brand flat file(for making or checking flat side), a new name brand 8” hone in the box marked for chuck only, a flat steel plate perhaps 12 x 12 with a piece of crocus cloth(for rolling off burrs), a hone for checking for flat side, a tray of block-ins from 1/16 to perhaps a couple 123 blocks. a few wheels mounted and dressed perhaps a 46 h&k. a 80J for needing a sharp corner and a 46k dressed to a 45* for corner chamfering.
Block-in (block or Parallel) should be touching high for tall work. The most important blocking is to the go side (the way the wheel pushed) Low blocks on the go side are often trip over block, a block bumping a part side that is not square so just bumping the very bottom is dangerous. Blocks on the other side often don’t help hold very much but do help bring more magnetism into the part. Consideration for how might the part turn is an aid to setting block-ins.
V blocks , angle plates, C and parallel clamps, set and angle parallels are often a tool makers personal tools.
Finding the work surface is important and dangerous because the work top (or other found surface) may not be flat or square so the found top (or surface) may not be the highest point of the part.. Don’s paper touch is good. With knowing the paper thickness you have some idea where the part is and that you might clear. We used to use the old IBM cards. With thinking you know you are clear best to come in from the grind side for a slow first pass over. Being on the grind side and going slow you can find a spark if too high with not having a pull-in wreck that would happen on the climb side.
With having the three lines of reference a job can be set true quickly and so often the grinder can be the fastest machine to get a job done.
With a sample part on the chuck a new part can be made with only using the sample for size reference, so very often a print and even measuring is not needed.
IMHO -
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11-11-2015, 11:17 AM #12
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Actually, Bob, I probably was not clear on my initial inquiry. I tried to say that many times I have removed 0.001" and consider it aggressive on my grinder (7" wheel on chevalier grinder fsg-618m with coolant). On those occasions, I have not done an in-feed on the table movement from right to left, but only because I was nervous about it, having heard of people being very surprised by the outcome. Originally Posted by rjs44032
Finally, you eluded that Don's downfeed of 0.001" was non aggressive. In my experience 0.001" downfeed was max per stroke. Until you get more familiarity with the machine and grinding processes I would stay at 0.0005". I never grind more that 0.001" on a pass and usually a couple tenths on finish if possible. Just my 2 cents.
Best Regards,
Bob
I am normally removing up to .0005" per pass, and have not been surprised by having my work piece go flying yet. I've never talked with anyone who personally had a wheel explosion attributable to this method of climb feeding.
Thanks to all who have replied. Great tips and things to watch out for on this subject.
Dan L -
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11-11-2015, 01:03 PM #13
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Grabbing when grinding in the "climb cutting" direction isn't a problem unless you let go of the table feed. If the work moves on the chuck, even in the conventional direction, it's more likely than not to pivot, putting the un-ground area under the wheel and forcefully ejecting it, possibly blowing up the wheel in the process. The moral of this story is don't let the work move on the chuck. Ever.
I do a lot of small mold insert work grinding dry. The enemy of surface grinding is heat retained in the work, causing it to expand and "suck up" into the wheel. The amount of heat that is building in the work is sometimes difficult to gauge, you'll be happily grinding back and forth when all of a sudden that orange stripe of sparks appears that tells you you've just glazed the wheel, burned the work, and probably blown your finished dimension as well. In-feeding in only one direction means the wheel should not hardly be cutting on the return stroke, just "sparking out", and there should be a noticeable difference in the amount of sparks between the two directions of travel. If there isn't, it means the work is getting too hot, and you are about to blow it.
Dennis -
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11-11-2015, 04:04 PM #14
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Grinding dry is frustrating because of the many stops to let the workpiece cool. It does not take much heat to ruin a part. Most people cannot accurately tell between 70 and 90 degrees by touch and that is plenty to cause a dimension change and if not evenly heated it will sguirm on the chuck. There is little you can do about it except wait. If your machine has provision for coolant, use it. It's much more productive.
Heat is real problem with plunge grinding. At one shop we made self aligning bearings for rod ends and such. One of the inspection techniques was to "pot" the bearing, immobilizing it in a clear resin and grinding it so that clearances could be measured with a microscope. One day I had a small one, not as wide as the wheel. I set the machine, a B&S 12X24 up to plunge.0001 on each traverse. I was busy at a mill when I noticed the change in the sound. The part had grown to the point that it looked as though it were taking .005. The coolant was boiling when it hit. All that heat from .0001 cuts with coolant. I'm sure that the wheel was not optimal but it opened my eyes about heat. -
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11-12-2015, 09:25 PM #15
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As others have stated, the workpiece should not be allowed to move on the mag-chuck, ever. Blocking in is highly advised on smaller/thinner parts. What is worth mentioning is also the type of material. I've ground a lot of hardened tool steel, most will readily hold to the magnet. The one material that, when hardened, does NOT stick well is D-2. It may seem to be on there but it should not be trusted regardless of the blocking and I would recommend holding in a vise(s) or some other mechanical clamping method. D-2 also has a nasty habit of heating up while grinding enough to cause problems, but that's another story. As other members have posted, heat can cause several different problems and is to be avoided. Coolant is a huge help if you grinder is set up for it. If not, an ersatz dam of modeling clay can be filled with coolant in some cases. I've used aluminum as a heat sink as well. To address your question about feed, for most general grinding I feed in both directions at the end of stroke unless it's the last pass for spark-out on a real close tolerance piece. For work that's +/- .0005 I wouldn't be too concerned with feed sequence. More concern should be placed on the part immobilization, heat, surface finish, and dimension control. How much down-feed will depend upon the material, thickness, wheel selection, the grinder, and how good a grip you have on the workpiece. Many times an EC has caused me to to have to remove more than .125 of hardened tool steel off a die block. I've ripped .003-.005 at a pass and wiped the dressing off the wheel. So long as you don't risk a safety hazard, thermal stress the workpiece, or burn the workpiece the last few .0001's are all (barring other factors) that matter. The only time I've seen a wheel explode was when an idiot dressed the sides of the wheel to a dimension and tried grinding that dimension between the long legs of a "U-shaped" part. After blowing up 2 wheels (he thought the wheel was cracked) someone pointed out the the legs were heating up by contacting both legs at once and "sucking" into the wheel. I've never exploded a wheel but have sent a part or two sailing off the chuck by not immobilizing it "Houston we have lift-off". Hope this was of some help.
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11-13-2015, 12:39 AM #16
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On the hydraulic grinder at work .003 with coolant and small step overs works fine feeding at both ends.
My manual one at home has ball ways and you can really feel it grab, rolling with the wheel at .001 depth.
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11-13-2015, 06:50 PM #17
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We use a lot of CBN wheels and if you can hold onto the part, .005 per pass is not uncommon in 60+ rockwell A-2, D-2, and powdered metals. Lots of flood coolant and a rigid machine and setup. With it trued and dressed properly a 6 - 8 microinch finish is do able with a couple tenths finish pass and spark out. Feed both ways all the time with manual or hydraulic machines.
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11-15-2015, 01:04 PM #18
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Thanks for starting this thread, great for us surface grinding newbies.
Question - when down feeding is it necessary to take up backlash? That is can one just continuously creep down, or do you go further down and then back up to your setting?
I have a Boyar Schultz 612 in pretty nice condition. -
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11-15-2015, 03:06 PM #19
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On a machine with an ordinary Acme lead screw the spindle should move down with gravity. If you try to remove backlash then it will fall the amount of the lash and at the worst possible time.If the spindle head does not easily follow the nut then something is binding.
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11-15-2015, 04:22 PM #20
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Page 2
It is so much easier to just down feed and most times it plain works. Originally Posted by richard newman
Thanks for starting this thread, great for us surface grinding newbies.
Question - when down feeding is it necessary to take up backlash? That is can one just continuously creep down, or do you go further down and then back up to your setting?
I have a Boyar Schultz 612 in pretty nice condition.
You hope for the spindle dropping to follow the screw and 80+% of the time it does.
At some point you no longer trust it and go with the down past, raise up method which is a pain in the ass.
Bob
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Thread: Surface Grinding Methods
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11-15-2015, 09:01 PM #21
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I like to feed out only and taper a lead in dress on the wheel.
One pass and done unless you get reduction on the way out.
Parts are parked where you can get to them I like to verify there was no reduction with a dial depth Mike.
If you get some spark from the tail put a lead out dress.
Than flip parts and grind to size same way.
I put the lead in with a top dresser and some times get several reductions with out having to flat dress.
I have ground miles of d2 slide gates this way.
Also if you grind this way you need to verify with a dro after a reduction that you did get feed and it matches the dial
Don't need any surprises when out in the part -
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A 3/4" wide rock and you can feed both in and out a long while - lots of passes before the land in the middle gets narrow using the small step over method. IME when it gets to about a 1/4" left its time to dress it of - back flat and start over, but thats a lot of passes on a 6x18" grinder, i really only end up finding it a issue if grinding something scaley. because generally i prefer to just chuck it on the grinder and leave it to it whilst i do something else than mill then grind! But thats the advantage of a hydrulic grinder i spose, its got no idea if your watching or not :-)
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11-17-2015, 06:00 PM #23
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Agree with TD There should be no backlash in a surface grinder head at down feed. Originally Posted by tdmidget
On a machine with an ordinary Acme lead screw the spindle should move down with gravity. If you try to remove backlash then it will fall the amount of the lash and at the worst possible time.If the spindle head does not easily follow the nut then something is binding.
The wheel head and motor are very heavy on most conventional grinders. They follow the hand wheel exactly. Still it is a good idea to test the free feed to tell the amount of wear in the vertical nut. The nut wears evenly and faster than the screw so size is not a major factor, also with wheel wear the down feed amount is relative to wheel break down. So the dal down is not always the same as the take.
The nut check is for safety. With extensive wear the nut can lock on the screw and on one occasion I heard of the head falling down.( not sure if that was true. Still set a soft board on the chuck with the wheel setting on, crank out the slack to just make feel on the other side of the wear amount .
With half the dial number free play plan to replace the nut. -
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11-18-2015, 11:44 AM #24
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Thanks for the replies. I have been just down feeding since I got the machine, and it's worked fine, but I thought I'd ask to be sure, considering we're dealing with tenths.
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11-18-2015, 01:25 PM #25
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Down feeding to skim the part full wheel with a fresh dress is one way to make tenths. This best with work only the wheel width to perhaps 2 time the wheel width. With needing two hits then a cross is good.
Down feed off the part then incremental across the part works also but can take more time..This often best way for wider parts.
With full wheeling I down feed on the grind side.
With incremental often cross on both sides with a slight pause off work..
Grinding wet or with a longer pause if the material needs this.. -
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11-18-2015, 01:34 PM #26
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Grinding precision parts, or any parts the grinding burr should be considered.. At one shop we placed a crocus cloth an a steel plate to slide the part in order to roll the burr off the set surface. Some jobe we would 45* the edge and then flat slide on the cloth. Yes at other shops a hone was used. Needing a sharp edge the burr is difFicult to manage so the wheel direction helps. .. But never using the chuck dressing hone.. it should be kept in the box and kept like new to be used fine side with oil.
- [machinist] Surface Grinding Methods, Lawrence London, 12/27/2015
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