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Tool Grinder

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Darren:
Hi Scott,

I'm certainly no expert on lathe grinding having never done it as yet. So others will join in and add their slant on this issue hopefully.

From what I understand grinding a shaft or say an internal taper on a lathe will achieve a higher degree of accuracy than normal lathe tools.

Polishing may make an item nice and smooth, but it ruins accuracy.

Also grinding may be the only way to work a really hard material. Perhaps just to remove the outer hardness on a tool or shaft. Then normal machining can presume.

Darren

bogstandard:
Scott,

Just to enlarge slightly on what Darren has said.

You are perfectly right to ask the question, and you have answered most of the question in your assumptions.

Like in the full size engine department, you wouldn't turn a camshaft or crank, basically they are too hard, so they have the journals and lobes ground. Because only very minor amounts are removed, the surface gets a very smooth and highly accurate finish (as long as the stones are dressed in the correct manner).

The pic I showed of internal grinding. That was being done to true up the collet chuck that I had fitted to the lathe, and needs to be super accurate to carry out precision turning. By grinding the hard nose where the collet fits, I achieved a 0 - 0 runout on it.

So say you wanted to make a one piece crank for an engine, you would rough machine the crank, leaving the journals slightly oversize. Then after the crank was hardened, you would grind the journals down to the required size. In your field, you could get worn journals on a crank reground, then fit undersized bearing shells.

The same goes for surface grinding, you can achieve perfectly flat, very accurate, highly smooth finishes on almost any material, including ones that you couldn't machine with normal tooling, ie solid carbide, rubber etc. You could also grind those materials on a lathe, if you needed a round profile.

So really, grinding is a specialist machinist job, whereas other trades have turners, fitters and mill operators, people are employed just as grinders.

BTW your accurate drill rod (silver steel) is ground stock, to achieve the accuracy required.

I hope this has made it a lot clearer for you.

John

SPiN Racing:
VERY much clearer!!

I had always heard the term referring to a different grind on a cam.. or re-grind a cam.. or re-grind a crank.
I never really put the 2 and 2 together to figure that out.

In my experience the only grinding I ever saw done around the house, was my dad with a bench grinder, sharpening lawnmower blades, and or chisels. ANd the grinding wheel was pretty rough.

In the race shop I do weekend work at.. they have a green wheel they use on one side of a grinder, and a wire wheel on the other. The shop owner will clean up the tip of a HSS or supposedly carbide bit.

I ended up buing a Carbide green wheel sharpener from Sears. It was around 60 bucks or so, turns slowly, and runs the wheel through a water bath. I have re-sharpened and changed the profile of some of the tools I have. But its not what were talking about here.


<taps chin>
Very interesting.

SO. THis beign the case..
My future project I want to build skills to be able to do. A Mini working Wankel engine, modeled after the Mazda rotary. Im thinking 1/4 scale off the top of my head. I am going to have to seriously think on my tooling, and procedures.
I know the Epitrochoid shape of the combustion chamber/rotor housing.. takes special work to machine. (Hourglass shaped housing) And the eccentric shaft.. aka crank shaft. shouldnt be too hard to replicate.. BUT.. I think it will be something that requires proper grinding.

<Adds info to the corner closet in the brain on things to compile info on>

sbwhart:
Hi Scott

I may be able to down load a bit of info for your memory banks, for when you start on your model wankel engine.

Below is a photo of a UK 50p  that has the same caracteristics to a wankel cylinder ie constant dia



How can this help you may be thinking, well a long ltime ago, when I had hair, I used to make the tooling for blanking these coins out (all within the law I may add). They were made on a specialist grinding machine for grinding taps, good quality ground taps have a radialy releafed form, in simple terms the grinding wheel goes in and out in sincronation with the rotary movemet of the tap. To grind the tools for the 50p we simply had a special cam made so that the wheel went in and out and generated the coin shape in the tool. The make of the grinder that did this was a MATRIX Coventry Thread Grinder, a compy that, like much of British Industry is No longer in buisnes but I'm shure that if you do a google search you will find some information.

I can also remember reading an article in Model Engineer about a modler that made/adapted a cylindrical grinding machine for grinding cams for model petrol engines he used a full sized cam as a master and by some cleaver mechanism scaled the movement down to produce a model cam, as I've only been reading ME for the last five years it is quite a recent article, but I can't remember  :hammer: exactly when

I hope this info will be of some help to you

Have
 :wave:
Fun

Stew

Divided he ad:
Did someone say miniature working wankel engine??!?!


How about this as a starter from last years Harrogate show..... Sorry you'll have to turn through 90' for one... I'll change it someday!











Hope these inspire?



Ralph.

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