Surface Grinder

[itsme]

Hi there,

I've decided that my next project is going to be a scratch built CNC surface grinder, as this will be extremely useful for a lot of the parts that I want to make in future. I have a few ideas about the machine, but need some help.

Firstly, some ROUGH dimensions. I will probably need about 400 x 300mm of table travel and about 100mm of z-axis travel. It will be used to grind iron, steel and aluminium (possibly other metals too).

I am planning on using ground bar (somewhere around 30mm diameter) with linear bearings to support the table. This is one of the cheaper options and I figured that it would probably be rigid enough for the application. The z-axis with the grinding wheel will probably use a dovetail or a profile rail (I'm not worried about this at the moment though). I am thinking about using a rack and pinion to drive the x-axis, as positioning accuracy is not too important and it will give reasonably high speeds. The y-axis will probably use a trapezoidal screw, as accuracy is not too important here either (but cost is). I think the z-axis (up and down movement) is the most important axis in terms of accuracy, as this determines the amount to be removed by grinding. For this reason, I think investing in a quality, ground ballscrew and good quality slides would be worthwhile.

When it comes to the powered grinding wheel, I have no idea. I don't know what size wheels are available for this application and I don't know what power and RPM I will need to drive the wheel. Any ideas on this?

I am also planning on grinding a fair amount of aluminium. As far as I know, this is not too much of a problem with the correct grinding wheel and RPM, but I don't know how a non-ferrous part can be held down accurately? Does anyone know how this is normally done?

I am obviously looking for the best accuracy possible. I would like the machine to be able to accurately move in increments of about 0.005mm so that I can get the thickness of parts spot-on. This would mean excellent alignment of all parts and zero backlash in the z-axis assembly. I'm not sure how close I can get to this, but that's the aim.

Finally, is a coolant system a good thing to have when grinding? It is useful to know right from the start so that the necessary spray guards/trays etc. can be built into the machine. I would imagine that dust gaurds are also fairly important.

Any thoughts on my thoughts so far?

Regards
Warren

[mxtras]

Sounds very reasonable - everything you mentioned seems spot on to me.

I would definately incorporate coolant - absolutely no doubt.

Nice project. Please keep us informed.

Scott

[Mcgyver]

mxtras, sorry dude, I’ve got to take the other side on this. itsme, this going to sound real negative, don't mean to be, but not giving it straight (as I see it least) isn't going to help anyone. Enough determination can overcome anything, so a lot of these remarks are in the context of how much effort and money it would take you and how inexpensive good used ones would be – buy a used one imo.

ground bars, nope unless they are supported, even then, don't like it. To get a good finish friction on the x motion has to be negligible and they have to have zero sag and be perfectly straight. Mine is on cylindrical rollers in V slots.

Backlash in z axis doesn't really matter; also don't know why you'd want a balls screw over a ground acme. The weight of the head with a high helix sounds like trouble.

Rack and pinion, hmmm to much mechanical bump and thump - use a simple capstan and wire like commercial units

Rigidity is a massive issue - this will determine the finish you get. Price out matched sets of ABEC 7 bears for the spindle (could be what 500-1000 cdn for a size large enough for a surface grinder spindle), the accuracy requirements of the spindle etc, and a used one starts looking good.

Regarding holding non ferrous, frankly, never done it. Making the really accurate stuff is usually in hardened (tool or case) steel or cast iron. Guess you'd use fixtures or a vice.

Finally, why bother with cnc? Unless you get real fancy and tie the grinding wheel dressing into it, seems like more trouble than its worth for common surface grinding apps

[itsme]

Hi,

Thanks for the replies mxtras and Mcgyver.

I've never used a surface grinder before, yet alone built one, so some of my ideas are perhaps not quite what would be considered 'normal' for a machine of this type, but I'm here to learn.

I have only briefly looked at used machines on the internet and most don't really seem suitable for home use. They all seem too big to fit in the garage next to my Micro Mill. Did anyone ever make any small surface grinders that were perhaps aimed at the model engineer? I certainly can't find any small machines for sale new.

Although CNC isn't necessary, I thought it would be fun - it's a hobby after all. Maybe I'll take a closer look at used machines and start saving in the mean time.

Thanks again
Warren

[DieGuy]

I just bought a nice old B&S hydralic off eBay for about $750. It has hydralic feeds and coolant. That is one tool you can get a bargain prices.

Non ferrous materials are usually fixtured on steel or held in a vise. For thin sections plaster of paris does work but is very slow to get ready and you must take real caution in depth of cut. I still have memories of pitching a table full of 304 stainless off a big Grand Rapids grinder, with pieces of the wheel flying around the room!

[Switcher]

If It was me, I'd buy a used Heavy Duty Surface Grinder on Ebay. The reason I say this is they are always on Ebay, Price is good, most of them will come with a few grinding wheels (used but still good) Also you will need the magnetic base (It should come with it) plus the older ones are very heavy duty! You will probably spend 1 weekend to make it look New! Most of them are old and ugly, but just need paint. I don't know about your power supply? With the cost of the machine & Shipping, you still be better off than trying to build your own. You can get a good vise on ebay also. You will need a very solid machine, "Chatter" will only mess up your wheels & material. This is one example from ebay. Good Luck

http://www.reliabletools.com/itemima...erM05/m09h.jpg

Save your money for Servos & Control. This was listed on Ebay starting at ($0.99)

Item number: 7550574081

EXAMPLE SURFACE GRINDER: (Small Footprint)

[ViperTX]

Well if the surface grinder dwarfs the micro-mill...get a larger mill....

[mxtras]

McGuyver - "ground bars, nope unless they are supported, even then, don't like it."

I don't care for them either. I agree that they would need to be supported and I more or less figured the grinder would be relatively small - knowing some of the projects itsme has shared with us.

I like the idea and have pondered building one myself when time permits. I doubt I would CNC it, and I would likely drive the table differently - maybe a hydraulic cylinder or a cable arrangement or something.

Scott

[Mcgyver]

Originally Posted by mxtras I don't care for them either. I agree that they would need to be supported and I more or less figured the grinder would be relatively small - knowing some of the projects itsme has shared with us. Scott

Having said that, I am building an unsupported ground bar cnc machine. Its very light duty - pcb mill, and mainly started to learn about cnc as opposed to setting the world on fire. Why I don't like it for a grinder is you need rigidity - there is the potential for the wheel will bounce along the work which would produce a lousy finish and might be dangerous – there is lateral and down force in grinding, no real up force.

There are home made grinders of various descriptions - Latuard in one of his books describes a surface grinder based on a surface plate and adjustable head on a column. The work is manually slid along the surface plate under the wheel - apparently high quality work can be done but that idea scares me!

Calling it a surface grinder and the given the tolerances seemed that he wanted something that, while perhaps smaller, was capable of a standard of work similar to a commercial machine. That’s the point where a little bit of knowledge about what goes into a grinder starts to make used look pretty good!

Mine is a small manual Norton, probably you can't get much smaller in a commercial one and that is NOT going down a set of stairs! There’s a pic here. http://www.cnczone.com/forums/attach...achmentid=6814

If you wanted a smaller machine, bench top size, what might make sense is a tool and cutter grinder. There are small ones and they can be pressed into service as a surface grinder, albeit with some big compromises but you also get a T&C grinder! Granted it might take some time and effort to find a small used one but they are out there. After having one, I wouldn’t want to be without, how quickly we get spoiled! Here’s mine
http://www.chevalierusa.com/Toolcutter.html Its still fairly beefy for a bench-top, probably 250-300 lbs – I had to disassemble to move it (done in the dark, in January in Toronto, crouched over and by the dome light in the back of a suburban!)

[itsme]

Hello again,

A used machine would be a great thing to have, but it still isn't entirely convenient. I have enough trouble with the 'senior' members of the family and a 40kg Micro Mill, so I'm not sure what they would have to say if I told them a 300 - 500kg surface grinder was coming...

Building one from scratch still seems appealing (for some odd reason). Clearly, the ground bar doesn't seem very popular, so lets rule that off the list. What about replacing this with 'profile' linear rails (I think that's what they're called)? I could probably also get away with reducing the travel quite a lot as well, which would make rigidity less of a problem (as well as cost). The aim would be to build something that is truly a benchtop machine. A ground acme screw would probably work well, but where do you buy things like that? I know where to get rolled screws, but I've never seen ground screws for sale anywhere.

I only have access to a standard wall socket supply. I don't have 3 phase and don't intend to get involved with 3 phase at the moment.

I guess I'll also have to think of an 'innovative' feature to add to the machine to justify building it myself... hmmm

Regards
Warren

[jleiwig]

I saw a website where a guy had bought the base and column of a mini mill from little machine shop and then adapted some sort of surface griding attachment to that. I believe it was a yahoo group for mini mills if i'm not mistaken.

[ViperTX]

Here's an idea so you don't have to displace them older folks....

Mount a grinding wheel between a lathe chuck and the tailstock (sort like a horizontal milling machine). Adapt, which basically means lengthen the crossslide for the length that you want to be able to grind. Use the compound to give you the width for the item that you.

I suspect that you could someway index the compound as you reach the limit of the crossslide.

Just a 2 sec thought...took longer to type out......this is rather interesting.