Surface Grinder

[Doc Hollywood]

Fitzo,

I have never heard a machinist use that lingo before, but I am sure you are right. I would imagine it does get tedious to keep up with and say all that in a single breath all the time.

What makes any of my statements incredulous Fritzo?

Doc

 

[Doc Hollywood]

No apologies necessary John.

I have never heard that lingo before from any of the machinists I have worked with, but maybe they just didn't use it with me since I was doing the CAD work and not the actual machine work. I guess there is code to everything depending on what end of it you are on.

I believe honestly I can hold a thousandth, and maybe better. To adjust for the idea of thermal expansion in aluminum I can use an alloy commonly found and cheap.....automotive aluminum heads. These things see over 200 degrees in the water jackets, and well over 1K in the combustion chambers. If it doesn't warp in 100K miles it won't go out of spec sitting on a stand holding a wheel.

Just to clean up the Z axis a bit I will be looking at linear bearing rods for support, and an ACME threaded rod for the up and down motion.

Now again I am asking. What horsepower rating are the motors that most of you have running yours?

I was looking at 3/4 to 1hp running on 110. That should be more than enough to run an 8 inch wheel shafted, and sitting in tapered rollers from an automotive application....

Doc

 

[fitzo]

Doc, perhaps it's regional, as most all the machinist types I know locally use that all the time. Took me awhile to get used to.

You said nothing incredulous at all. I specifically meant the fact that originally saying you could home-build a surface grinder that would hold to a "tenth" was met with some incredulity. Terminology differences. Me included, 'cuz that's (0.0001") awfully tight tolerance for anything but one hellacious machine, as you pointed out.

I for one am anxious to see what you come up with. Nothing like a challenge to inspire.

I checked the "motor plate" on my grinder. It's funky old aluminized paper and when I wiped it with acetone it got trashed. Sorry, but I can't give you a specific number. It IS under 1HP, though.

If you haven't done a lot of surface grinding, I'll point out that one of the biggest problems with surface finish comes from chatter. The bearing supporting the wheel shaft will need to be really tight, and the headweight large. Another problem encountered is keeping the ways moving smoothly. There's a way oiler on mine, but I found out early that one must use the oil judiciously, or it floats the table and accuracy goes all to heck. Just some observations I hope help in your design.

 

[Abrasive]

I think you're going to run into surface finish problems if you build an aluminum-bodied surface grinder. Cast iron is much more massive, and has far better vibration-dampening properties. I think an aluminum unit would sing like the dickens, and you'll see it in the surface finish.

I am all for doing rather than talking, though, so if you want to give it a go, I say do it!

The only other thing I'd add is to be careful. Make sure your (wheel) downfeed is precise and repeatable. You do NOT want to tell the thing to feed down 0.0005" and have it drop the wheel a few thou instead. Very bad things can happen. A thousandth or two of an inch on a lightly constructed surface grinder is a heavy cut.

Running a surface grinder is an art. There are many variables: work hardness, wheel composition and hardness, wheel size, wheel RPM, infeed rate, traverse rate, wheel finish (how fast or slow you've run your truing diamond across it). Plus the variables that are tougher to control: spindle bearing type and condition, condition of table ways, motor vibration. All of these will affect surface finish and accuracy.

 

[J. MacDonald]

Yeah, surface grinding is certainly an art. So many things can affect the outcome. From what I know, ball bearing ways are generally more accurate than V bed ways for supporting the table. What's used to move the table can also have an effect. Hydraulics are generally thought to be best, and usually allow for some controlled power feed. Cable actuation is next in line for smoothness and the last choice is rack and pinion as the action is coarse enough that you can sometimes see the rack pattern come through on the work surface.

I'm sure it was my incredulity that Fitzo was referring to as I was incredulous at the thought of a home built aluminum machine holding a tenth (.0001). Every shop I've ever worked in and every machinist I've ever spoken with would understand a tenth, or a couple tenths to mean ten thousandths of an inch. I haven't played with my little old used Yuasa 6x12 surface grinder enough yet to be able to judge it's accuracy, but I'd be shocked if I can do much better than .0005 as it's not the biggest and most rigid machine around. For a surface grinder it's pretty light weight at around 700-800 lbs. I believe it's 3/4 HP but it's three phase 220 running with a static phase converter off single phase 220.

An aluminum head might not warp, at least when torqued down correctly. Get the torque out of sequence and they will warp pretty quickly. They certainly do experience thermal expansion and contraction. There's a pretty common practice in machinig and fabrication known as a shrink fit. When you need two parts to go together really securely, you machine them to pretty tight tollerances and then freeze the smaller one and heat the larger one to a couple hundred degrees in an oven, then slip them together and when the temprature equalizes the parts are joined so tightly that it takes a pretty good sized press to seperate them again. This is well documented. One of the fellows over at www.practicalmachinist.com even posted the formula for expansion sometime back so you could figure out exactly how much variation you could count on at various temps. I think it was Forrest Addy who is an old machinist that should be looked upon as a national treasure. That guy's forgotten more than most machinists will ever learn about the trade.

I'm curious enough now that I might have to take a 2" aluminum block and freeze it, then measure it with a mic and then heat it in the oven and measure it again to see if I can measure the variation.

Good luck with your project.

John

 

[Doc Hollywood]

I had wondered about the oiling situation, and how to keep the crap out of the ways. This is definetly going to be something to reckon with. I am thinking a sheet of automotive rubber gasket material can be fashioned into something that can be used to keep the larger stuff out. Gib adjustment won't be so much a problem, but keeping the ways free of trash is going to be a big deal as stated before.

I have figured out a way to include a coolant pump setup for the unit. The only issue I have with that is the spray of coolant getting everywhere.....messy stuff.

The stone carrier setup I am most likely going to overengineer so as to make sure I can hold a decent tolerance. I am hoping for .0005, but we will see where I can get it. I am looking at mocking the whole thing up in wood...not a working mock-up, but something to model off of. Will post pics when I get that far.

John....I have the gingery set of books, and several others that he and his son Vince wrote on other machines. I am impressed at how they followed the very old school way of doing alot by hand, and the use of scrap for alot of it.

I have contacted Vince (since Dave is no longer with us) about designing and building for a nother book a wire EDM machine, and a cathode EDM. I am hoping to offer some assistance on the wire setup, and I think it is doable with scrap stuff as well. I am going to the plastics shop to look at the cathode machine in the next few days.

The cathode machine makes me nervous for a small shop because of the dielectric fluid. In Korea they use Kerosene, and here we use a less flammable dielectric. I am worried about flash fires from the fluid more than anything. Looking for a more viscous/higher flashpoint fluid to use. Any suggestions?

Doc