Surface grinding finish

Hello all,

I have renovated a Herbert manual surface grinder and it performs well BUT.

The surface finish I get is very flat, but looks a bit like fish scales or very very fine serrations.

Does anyone have any suggestions as to the cause for this surface finish? I thought that the long drive belt may be causing some kind of speed variation due to its tension. Is it something I am doing wrong on the speed of feed or depth of "cut"? Obviously I have no way to check the speed I am traversing the work at but fast or slow does not seem to make much difference.

Any thoughts or ideas gratefully accepted.

Regards T

Could be the drive system but since it presumably worked ok in the past I'd look elsewhere to begin with .

The most likely cause of problems is that the wheel is not dressed properly .

I have also struggled with surface grinding. I have managed to get reasonable results by trial and error. This surely would make a good article for MEW. I would be interested to know how often should the wheel be dressed and how do you compensate for wheel wear?

David

Hi Tractor Man

Had similar trouble when I renovated my eagle grinder (seen on www.lathes.co.uk/eagle_surface_grinder ) I fitted a powertwist belt with a belt tensioner which improved things but did not eliminate it, then fitted new spindle bearings which did likewise. Finally stripped it all down and discovered that the hardened spindle was slightly bent, about two thou in the middle. This caused shaft whirl at 2800 rpm which caused wheel wobble, even though the wheel was diamond dressed on the machine. Made a new spindle from EN8, ground all over, which provided a complete cure. Surface finish is now impeccable.

The bent shaft could have been caused by heat treatment during manufacture, but I suspect some clown lifted the machine with a sling around the shaft (not me I hasten to add).

Hope this helps

Jim

p.s. copy & paste the url, doesn't seem to work from within the post

Edited By Jim Cahill on 10/04/2012 15:16:31

Hi Jim,

I think the "_surface_grinder" needs to be left of the URL

I think this is it.

Les

Have you balanced the grinding wheel and are you dressing the wheel with a diamond? Other causes could be the wrong grade wheel for the material being ground, or play in the head bearings

Check balance of wheel, and dress wheel with a dimond, when you dress it travers the dimond across the wheel slowly at the final pass take it across a couple of times at the same setting.

Stew

Check balance of wheel, and dress wheel with a dimond, when you dress it travers the dimond across the wheel slowly at the final pass take it across a couple of times at the same setting.

Stew

It's a long time since I used a surface grinder but I would make sure the wheel is of a suitable grade. I can't exactly recall the wheel spec. but 46 I springs to mind. Wheels that are too hard tend to bounce. Colin

Many thanks for the posts so far, The spindle is mounted internally and I don't think it could have been subjected to bending forces as described by Jim, So I am hoping there will be no need to replace it.

I recall the bearings were fine so they were not replaced, I am hopeful that I have refitted and adjusted them correctly but that is a check I will complete after I look into the wheel grade and balance/dressing of the wheel. Thanks for the advice on dressing, I am using a properly mounted diamond dresser and following instructions but may be rushing the process.

I fitted a single slack adjuster on one side of the belt but this made only a slight change to the finish, I am going to fit one to the other side to control slap on that long run too as it was a simple mod to do.

I will report back with any progress but is there any comment on speed of traversing the table? I have seen a you tube clip where the table is motorised and literally flies back and forth, what is an advisable speed to work the lever back and forth?

RegardsT

You should not be taking more than a two thou depth of cut ; for a good finish 2 or 3 tenths of a thou is about right. Table speed about 3 ins per second should be satisfactory. Colin

Hi Tractor Man

I found this anonymous article from Practical Machinist from 2002 which I think is very useful.

http://www.practicalmachinist.com/vb/greatest-hits-links/surface-grinding-deeper-cuts-better-finishes-110659/

regards

Jim

Hi all,

some success with the problem I posted about. I was using a 60 grit wheel and I dressed it according to advice and the finish was markedly better.

Seems the feed and table speed are a dark art so plenty of experimenting to get the right feel.

But I changed to an 80 grit wheel and dressed it and things are a great deal better. Very much smoother and visibly superior to the best efforts with the 60 grit.

I took off the drive belt and the shaft feels smooth and free running to me but I could be wrong so I might have a go at re-adjusting the bearings.

I will also make up another belt tensioner this weekend and report back when that is done.

The original 3 phase motor is long gone and a clarke single phase has been substituted, could that be causing problems? Have read other threads that suggest phase converters on three phase can cause issues with surface finish as the motor does not run dead smooth.

Not sure about deep cuts and shallow feeds as the machine has no coolant provision so heat might become a problem.

Thanks so far.

Regards T

Hi There

A60K5V or A46K5V for the wheel.

If grinding a magnetic chuck, steel and brass, you will get good results with a silicon Carbide wheel.

Dressing the wheel

The diamond should be at an angle to the wheel so the grit is torn out leaving it sharp. If you juist wind the wheel across the top of the diamond it will be blunt.

Dress the wheel as above and then relieve the wheel across 2/3 to 3/4 of its width by about 5 thou deep like this ------------___ This takes the load off the face of the wheel.

Maximum depth of cut would be about a thou although we used to take 60 thou cuts on cast iron.

regards David

Edited By David Clark 1 on 12/04/2012 09:23:16

Hi David,

If I read correctly you're recommending a silicon carbide wheel for grinding steel? I'm trying to surface grind some steel (low carbon, hot rolled) at the moment, and while the opposing faces feel flat and I cannot measure any difference in thickness there is definitely a fine, but regular pattern on the surface. I'd assumed that it was due to the wheel bearings being knackered, but might it be due to the wheel skipping? The wheel I'm using is white aluminium oxide, 46 grit, I can't read the rest of the description but I think it was medium hardness.

Tractor man: A single phase induction motor has a pulsating magnetic field, which may, or may not, affect the surface finish. A 3-phase motor does not have this pulsating effect. There are those who state that a single phase motor can affect the finish when using a lathe: I would have thought that a surface grinder would be more sensitive. I'm using a 3-phase motor, as I have a 3-phase supply. My grinder would have originally been supplied with a single motor driving both wheel and table feed (all mechanical) but had been converted at some time in the past to two single phase motors, one for each. The wheel drive motor smoked soon after I got the grinder, so I threw the whole lot away and reverted to a single 3-phase motor driving everything.

Regards,

Andrew

Hi Andrew

No, I did not recomend a Silicon Carbide wheel for steel.

I recomended it for a brass and steel magnetic chuck. the one where the brass and steel interleave.

regards David

David: Now I reread your post I see that I mis-understood. I'll probably buy a silicon carbide wheel anyway, as I need to clean up the top of my magnetic chuck.

Regards,

Andrew

Coolant will help a lot too.

Takes me back a few decades mainly Snows, excellents responses above.

I have the same Herbert grinder, called the Junior.

I converted mine to a Clarke flange mount single phase motor many moons ago, and it works perfectly.

There are no need for tensioners on the belt. I am still using the original belt that came with it, but on it's next overhaul, due fairly soon, it will get a new softer link belt.

BTW, check that your belt has no 'set' in it, where it has stood for some time. because the pullies are rather small, the belt can get little 'humps' in it where it has sat over the pullies. Mine did, but after an hours running, they disappeared. Because surface grinders are not used as often as normal machines, I would do a fairly long warmup run when coming back to using it, just to straighten out the belt.

Mine , when I first got it, used to leave a very bad surface finish, but that was cured by cleaning out the bearing head and giving it the correct preload on the bearings. General rule on that, tighten up until no end float at all (use a DTI), then give the nut a further 1/16 th of a turn. ALWAYS lets the machine run up for at least a couple of minutes before use, to allow the spindle to expand to it's operating length. I normally give it about quarter of an hour, just to be on the safe side.

There is no way on this machine to balance the wheel, but with careful dressing, I have never found a problem with it. I dress and use mine exactly as in the link that Jim provided.

Grinding vertical surfaces can be a bit of a problem because you have no dials on your crossfeed handle (unless you have the deluxe model), but a dti can be used for that problem, or do as I am about to do, fit it with a proper DRO. Even though my machine is old, it is perfect for what I want it to do, and fitting DRO's will make it much easier to operate.

2 thou MAX depth of cut, but if possible make that 1 thou, and a couple of tenths for a finishing grind and sparkout.

If you email me, I should have somewhere, a few pamphlets on this machine that I can let you have in PDF format.

John

Again some really helpful posts and a lot of experience shared so many thanks to all who have contributed.

My machine does have cross feed dials and I fitted a DRO to the Z axis so I can gauge depth of cut, but it only reads down to five tenthous so its hard to get really small finishing cuts, How do you do that with such a course lead screw on the column?

I also found quite a bit of movement in the table gibb so I will adjust that tonight to ensure smooth operation with no possible vibration etc.

I'll also try to reset the spindle bearing as I did not have any information on doing that when I rebuilt her.

Onwards and upwards, T