How do I get a decent finish?
|52 forum posts|
Does anyone have any hints and tips for using a toolpost grinder. I've been messing about with a grinder for a mini-lathe but can't get a particularly good finish. The grinder has an 80 grit 80mm wheel. Is 80 grit too coarse for a smooth finish?
The photo is a blank arbor that I've ground first dry all the way along and then the outer 2/3 or so was ground with some lubricant which gave a slightly better finish. The lathe was running at 2500rpm and in the opposite direction to the grinding wheel.
I found a previous thread where Graham Meeks comments have disappeared and it never really came to any conclusion so any additional hints and tips would be welcome.
168 forum posts
The first thing to do is lose a nought off the lathe spindle speed. 250 RPM would be a much more realistic work speed for grinding something that diameter.
|Ian S C||27/02/2015 09:34:34|
7468 forum posts
Scott, go to the search window, and first put in tool post grinder, read. Then grinding.
I think you want nearer 180 than 80 grit, but you need to read up a bit about grinding, different grades are used for different steels, basicly the harder the steel, softer the stone. To get a good finish you must dress the wheel before use, and lock the cross slide, and very light feed. What power does the motor on the TP grinder have, and what revs does it do.
Ian S C
|52 forum posts|
Thanks Steve. Tried various speeds this morning but not much improvement.
Ian, I was coming to the conclusion that, as you advise, I need a finer grit wheel to get the finish I'm looking for. I did dress the wheel but that didn't make much difference. Trouble is the wheels don't seem to be a particularly common size (80x10x20). The grinder is 250W (input) running at 6000rpm
|Clive Hartland||27/02/2015 10:00:07|
2810 forum posts
My experience of Lathe toolpost grinding is a slow speed for the job, I seem to remember about 150 rpm and excceedingly fine cuts in the order of under a thou.
Do not dwell on the cut and make sure if yo have a shoulder you undercut the wheel to only give a small contact at the shoulder.
Work with coolant as i will heat up quickly otherwise.
|Nigel McBurney 1||27/02/2015 10:31:10|
999 forum posts
I once owned a Jones and Shipman cylindrical grinder, I found that the work speed should be 100 to 150 rpm on a small shaft, fine grit wheels and flood coolant ,the coolant has lot less soluble oil in it ,than the usual 20/1 try 60/1 or 80/1, a cylindrical grinder which is very heavily built compared to a lathe allows final cuts of one or two tenths of a thou to be taken. The only time at work that I ever used a toolpost grinder was in an 8 in Wilson lathe grinding a long rubber coated print roller, awful job , fine black rubber dust got everywhere took as long to clean up as it did to do the job, I would never use a toolpost grinder on lathes that I own, too greater risk of grinding debris getting on or in the slides.
|Jon Gibbs||27/02/2015 12:01:34|
|739 forum posts|
Do you need a toolpost grinder for what you are doing?
If it's just a better surface finish you're after then how about a vertical shear cutting tool?
It was new to me but is very handy for finishing cuts and doesn't suffer the disadvantages of grinding.
|52 forum posts|
Absolutely don't need it in the slightest. Was just messing around with the thing to see if I could get a decent finish
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