Finishing piston o.d. with toolpost grinder

[Rich Carlstedt]

Brian
Cover the Lathe ways and carriage with Plastic film/sheet and then lay wet paper towels on the plastic.
The abrasive dust will stick to the wet paper and cleanup is a breeze as you just fold up the plastic and discard
Rich

[luthor]

A TPG is a very handy piece of equipment to have in a home shop, I purchased one for around $300 Australian dollars a few years ago to grind the #40 taper in one of my milling machine spindles. I have not used it since but I am sure it will get used again in the future.

[Mcgyver]

A toolpost grinder can do easily 90% as well as a "real" grinder,

A real grinder is a world of difference. Much heavier and better balanced. Its going to have finer infeed and the biggy, the adjustable top table. That's what lets you fairly readily get things with a tenth the same diameter over there length. About impossible on a lathe. I regularly cylindrically grind for finish and accuracy but rarely grind on the lathe, its imo 10% as good not 90%.

I agree grinding imposes a low pressure but its not zero. At the same time, setting of for really accurate turning (super sharp tool and 10ths infeed indicator), how much force do you think a 2 tenth DOC imposes? not much, and even then, whether this at all matters will vary part to part. I did a bore yesterday, wanted 5 micron clearance between it and its mate, got 7 turning it. Grinding would be a better finish, agreed, but I doubt it would have made it any more accurate and possibly less so given the shake rattle and roll of the typical TPG (and dumore and wolf, not exactly junk, but still brings way more vibration than a proper grinder) adds and the lack of flood on the lathe (in my case).

Where I do sometimes grind on the lathe is internal stuff. But its still dicey compared to a grinder. Even went so far as to build a 2 plane dynamic balancer to get vibration out of the system. That improved it but its still the really poor cousin to cylindrical grinding (which btw I do on a tool grinder which is the poor cousin of a proper grinder...it is however scraped into perfection, ground up, so does really accurate work). The last internal grind I did I used an air pencil grinder which actually work quite well.

[Doozer]

I have a Brown Sharpe #13 grinder, a Covel 512 grinder and a Heald #7 ID grinder.
I can say the difference between a toolpost grinder and a cylindrical grinder is like
a Yugo and a Mercedes.
I have a 1933 Van Norman Piston Grinder for sale cheap.

---Doozer

[J Tiers]

With the TPG, you have to NOT apply much pressure, and you have to spark out a lot.

But the job can get done.

The Yugo will get you where you are going. It's just not as much fun to do it with the Yugo, and it goes slower.

[eKretz]

There's no question that a machine built solely for grinding is better, and easier to use. As I mentioned, to get a TPG to do its best, you'll need to take care to get everything right, and that may include trying a few different approaches with rotation direction, RPM, FPM, dressing, wheel type, DOC, feed, sparkout etc. But a TPG absolutely can do almost as well as a "real" grinder - I've done it plenty of times. I've also run plenty of "real" built for purpose grinders and am not denying that they are better -mainly in ease of use, and rigidity. Exhibit 1, have a look at luthor's photo. Doesn't get much better than that.

[luthor]

Getting back to the question asked by the OP, a TPG will do the job nicely although I am not familiar with the Little Machine Shop product, it looks a bit lightly built. For cast iron I would use a Norton 39C60JVK grinding wheel or finer grit, 80 to 100 maybe if available.

[luthor]

Is it just me or has anyone else ever wondered why someone would put up a post asking for comment and then, even after many replies, doesn't bother to check back in to the thread?

[Sparky_NY]

Is it just me or has anyone else ever wondered why someone would put up a post asking for comment and then, even after many replies, doesn't bother to check back in to the thread?

Pretty standard procedure for Brian. I am pretty sure he reads the replies just does not comment very often at all. On the surface it would appear he ignores the suggestions/comments but I don't think that is the case. So, he probably checks back in but just remains silent.

[brian Rupnow]

Luthor--I really do read the comments. I posted this question on three forums and have a very wide range of answers. I post a lot on this forum, and really do read the answers. Sometimes I just don't have anything intelligent to say.---Brian

[Sparky_NY]

Luthor--I really do read the comments. I posted this question on three forums and have a very wide range of answers. I post a lot on this forum, and really do read the answers. Sometimes I just don't have anything intelligent to say.---Brian

Reminds me of the annular cutter thread..... tons of suggestions for you to get/use them and not a peep of a response from you. THEN...... a bit later you showed the new annular cutters you bought.

[J Tiers]

Bottom line...... While I am not a fan of the grinder you have (based totally on looking at pics), it ought to be able to do a good job of sizing the piston. I think it would work better on a CI piston than aluminum.

With my Dumore, I find it useful to; 1) use a wheel that is finer than the usual ones, and 2) run the lathe quite slowly in the SAME direction as the wheel, so they are moving parallel where it contacts the work, not opposite as is suggested by most. No idea what that does, other than give better results for me. I have an impression that it led to less "chatter".

[brian Rupnow]

I asked this question because I want to bring a cast iron piston down to just a couple of tenths under the bore of a cylinder. I created a split external lap to use as well. So far, I haven't used either. I'm gathering information, thank you to those who gave an answer.---Brian

[eKretz]

If you are going to run it that close you might want to lap both. Better chances of getting as near to dead straight as possible.

[brian Rupnow]

The only issue I have with grinding the outside diameter of the piston, is that once the piston stock has been removed from my lathes 3 jaw chuck, it will never go back in the same way. My chuck has about 0.003"total indicated runout. What that means is that getting the piston back into the chuck exactly as it was before depends solely on good luck. I'm not sure that would really affect the way the piston works or not. If I use an external lap to bring the piston down to size, it doesn't really matter if the piston is exactly centered in the chuck or not, because the external lap is free floating and is held in my hand.