Surface Grinder

Tom Militano

Tom Militano

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Feb 27, 1999
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I was looking at Jens Anso's post on his homemade surface grinder and thought I might look into that myself. I have a very high dollar, precision, crossfeed table, about 100 pounds, that a friend gave me. It has adjustable gibs, grease fittings, and is graduated in .001 increments. It has seen very little use. I can rig up a dial indicator that's graduated in .0001 that's in one of my toolboxes. Yup, next project after I get some knives finished up and out of here. I had a large surface grinder, with power feed, that I paid $500.00 for and it took up half of my shop. Somebody with more money than brains wanted it bad, I mean really bad, and when he was done counting out greenbacks it was his.
 
The Harbor Freight surface grinder is well worth the $950 I paid for it. It needed some very minor tuning and a decent stone. It is as accurate as you will ever need for folders. It fits easily on a sturdy bench. I'd recommend it to anyone looking for a low buck grinder.
 
It would seem like you could build one on the cheap. I may be wrong, but it looks that way.

What speed do the motors run on the harbor frieght unit?

Doc
 
Tom: Remember I also built one it's cost was around $600, thats including the Kalamazoo grinder. Pic on website.
 
I found a nice little Yuasa 6x12 manual surface grinder for $700.00. For that kind of money it hardly sems worth the hassle of trying yo build one and maintain the critical dimensions.

John
 
the one I built costed me around 250 total which includes the base machine which allready had the slides and precision needed, chuck and wheels.......but I was lucky and found the machine for something like 75$......
 
Call me stupid, but can someone define the "critical dimensions" necessary to make the grinder work for surfacing? It would seem to me that if the stone were true, and you had a mechanism to raise and lower the stone taht was accurate, and a way to feed the work into the turning stone it would seem like you couls build one from scrap and a good quality stone.

I will have to go look at the one that is at my old workplace. I think I can come up wiht a way to built it for under $200....

Doc
 
What is a good replacement wheel for the Harbor Freight surface grinder? In particular grit and color?
 
Doc:

You hit it on the head. If you had a way to predictably raise and lower the stone and a way to predictably feed the work into the stone, you would have a perfectly good surface grinder. The critical dimensions I refered to are the ways that allow for the repeatable precision presentation of the stone to the work piece. Feeding in a half a thousandth of an inch is not something that can generally be done with any repeatability on a machine welded up out of angle iron, nevermind getting a smooth finish. I'm by no means bashing Jen's original idea, just voicing my opinion. In building a surface grinder, the wheel is only a small part of the equation. Wheels wear and are thrown away. The precision part of the mechanism is generally big pieces of cast iron that are engineered to allow you to place a disposable wheel into a precise position relative to the workpiece to make the final product.

John
 
Here's a pic' of mine

16-Home_Surface_Grind.jpg
 
John L said:
What is a good replacement wheel for the Harbor Freight surface grinder? In particular grit and color?
Click to expand...

John, I used to use the red stones from MSC, made by Colonial Abrasives. I have found that 46 - 60 grit work the best. For the most part, I used the 46H ruby, Colonial part number 65878324. They worked well, but not as good as belts.

I have converted my grinder to use 2" x 72" belts and will never go back to stones. With a good selection of belts I can hog or finely grind all types of material. I use carpet tape to flatten handle materials and non-magnetic items. The belts make grinding very, very fast. I do not have a way to host photos, but if you want to see some, email me and I will send them.
 
jmxcpter said:
Doc:

The critical dimensions I refered to are the ways that allow for the repeatable precision presentation of the stone to the work piece. Feeding in a half a thousandth of an inch is not something that can generally be done with any repeatability on a machine welded up out of angle iron, nevermind getting a smooth finish. </QUOTE>

half a thousandth may be a difficult goal to attain for what I have in mind, but I bet I can get it within a thousandth, and I am going to make the pieces from aluminum to boot.

Let me make sure I have the makings correct here. We need a true flat surface for the work table...along the lines of polished granite flat....no problem. An electromagnet to hold the work to the table....no problem. A quality grinding stone (I know this part will wear out quickly, and that is to be expected), and a way to move the stone into the work in an accurate manner. Hmmmmm...I think I can do all of that and I can do it for under $200 bucks. I am currently building a lathe, with power feed, and change gears, and the works will be under $250. The swing and length should be in the 7"swing x 28" travel range.

Let me see what I can come up with, and I will take the challenge to build the sucker. This has now become a good one. I gotta try this for myself....hahaha.

<QUOTE>In building a surface grinder, the wheel is only a small part of the equation. Wheels wear and are thrown away. The precision part of the mechanism is generally big pieces of cast iron that are engineered to allow you to place a disposable wheel into a precise position relative to the workpiece to make the final product.
Click to expand...

Unless you can predict the rate that the wheel will wear (not entirely possible) then it would be hard to assure that the grind would be uniform across a large amount of surface. I do agree that you should be able to accurately gauge how much material you are removing from the surface initially though, and that if the grind is not excessive that it should be fairly accurate for the entire length of the work.

What rpm are these motors turning on the commercial units? What horsepower are the motors? I do need these two factors as well as whether the unit it being pulley driven and the speed stepped up or down or if it is a direct drive.

This is gonna be fun!

Doc
 
While I don't doubt that you could, and might, build a servicable grinder out of aluminum for very little money, the practical reality is that aluminum is not well suited to the purpose. Cast iron is much more rigid and thermally stable than aluminum. There was a fellow named Gingery who recently passed away that had published a whole series of books on how to make machine tools from home cast aluminum. He not only built the machines, but some pretty amazing projects along the way. I'm not disputing that it can be done, only that it's not the most efficient way to get the job done. If aluminum could be made into a decent surface grinder on a commercially viable scale, someone would have done it by now. The coefficient of thermal expansion of aluminum makes it unsuitable for a grinder that would be useful for anything considered repeatable and truly precision. Even with cast iron, in most precision shops, the temprature is closely regulated as it affects the precision the machines are capable of (68 degrees is the standard). I realize that this level of precision is not necessary in building a pocket knife, but a surface grinder should be able to hold a couple tenths on a repeatable basis and I doubt yuo can achieve that level of repeatable precision on a home built aluminum machine.

John
 
All I can say is we will see.

Imeant to go look at one at harbor freight today and forgot. Oh well, there is always tomorrow.

A tenth should be easy to maintain. None of us here are doing major production work either, so there is really no reason to spend a huge amount of money on the machine that sees what....a half hours use or less per blade? I don't know about the rest of you, but 500 bucks is big stuff to me.

Doc
 
I've got a line on 2 American made surface grinders that need some tune ups.

My pick for $300........What are these used for, anyway??

Mike
 
The purpose of a surface grinder is to be able to hold move the workpiece into the wheel in a very controlled fashion on all three axes of movement allowing you to take very fine cuts. Unlike a bench grinder or traditional belt grinder where the workpiece is usually held in your hand, the work on a surface grinder is usually held on a magnetic chuck which is very flat and used as a known flat starting point. A good surface grinder with someone who knows what they're doing can hold tolerances of .0001 inch or even less with the right combinaiton of machine and operator. Doc's claim to be able to build a machine at home that will hold a tenth (.0001) indicates to me that he's either way more talented than I gave him credit for, or he's never really tried to do anything that precise. Holding a tenth repeatably is really quite an achievement. Even the machine that Jens built originally started as a piece of precision machinery that he modified and Jens is very talented. He's been quite an inspiration to me in some of my home shop projects like the 2x72 belt grinder I'm building.

Basic uses are to make things very flat. With flat work pieces like knife blades and handle slabs they're very useful in not just making the surface very flat and smooth, but parallel to the opposite side and uniform in thickness which helps in making a knife with a smooth action. More advanced uses are grinding grooves, compound angles with the right tooling and even very precise cutting.

I worked at one small shop in high school where we were cutting ferrite on a surface grinder with a thin diamond wheel (expensive wheels). That was a dirty ugly job. It really ticked the boss off when I tried to rush a bit and destroyed two of the diamond wheels (oops!). I ran surface grinders at a couple other shops during my short career as a machinist many years ago. The grinding room was always grungy as precision grinding generates fine dust and is usually accompanied by flood coolant that makes for a filthy goo. I wish I had the room in my tiny shop to keep the grinders seperated from my mill and lathe, but life is all about compromise.

John
 
jmxcpter said:
A good surface grinder with someone who knows what they're doing can hold tolerances of .0001 inch or even less with the right combinaiton of machine and operator. Doc's claim to be able to build a machine at home that will hold a tenth (.0001) indicates to me that he's either way more talented than I gave him credit for, or he's never really tried to do anything that precise. Holding a tenth repeatably is really quite an achievement.
Click to expand...

Well John, I am going to point this out and I am not trying to be a smartass either, but .0001 is not a tenth....it is a tenthousandth of 1 or 1/10000. There are major companies who make machines and measuring equipment that can't stay in that kind of tolerance for a given price. I doubt seriously a surface grinder you buy for under 10k is going to hold that kind of precision.

On the other hand 1/10th expressed as .1 will be easy to hold to, and I expect that I can make a machine that will hold 1/1000th easily or .001.

Aluminum doesn't expand as much as you think it does, and I have worked in several shops that were doing very precision work and found noe to be climate controlled to any degree other than to keep the machinists happy.

Doc
 
Doc, most all the machinists I know use a shorthand lingo wherein they speak in terms of "thou", such that a "tenth" to them means "one ten-thousandth" and 1/10" would be "a hundred thou".

There's just a difference in terminology here, and thus the response of being slightly incredulous at a "tenth" from a homebuilt apparatus.

When I got my Taiwanese surface grinder 20 years ago (from Enco), the master modelmaker machinist who helped me set it up brought all his indicators ready to prove to me what a piece of crap I'd bought for $700. We were both quite surprised when it indicated in at .0003" (three "tenths" to him) or less after we'd shimmed and surfaced the magnet. After all the use it's seen over the years it'll still grind to within 5 "tenths". Not bad for a non-coolant machine with $7 wheels.

I bought $200 worth of fancy Norton wheels earlier this year after reading what others used on a thread here. They would probably create a hell of a finish on a high-precision machine with flood coolant. I didn't like them at all. My personal preference is the white carborundum open-cell 36 and 60 grit wheels, the cheapos. With frequent dressing I get a pretty acceptable surface.

I'd like to switch to belts one of these days, to surface damascus.
 
Doc, my apologies. You're right. Aluminum certainly doesn't expand enough to throw you off if you're trying to hold a tenth (.100 inch) but will certainly cause you grief if you're really trying to hold a tenth (.0001 inch). As Fitzo noticed it's just a cross up in terminology as I was using what I'd generally understood a tenth to mean in precision metal working. Holding a tenth (.100 inch) isn't so much precision metal working as it is carpentry:)

John
 
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