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Doc Nickel
03-31-2019, 12:19 AM
Buddy of mine has a Grizzly G8689 desktop mill, that a previous owner had converted to CNC, but had cut a few corners. (I've mentioned it here a few times already :D )

I'm rebuilding the mechanical side in exchange for his helping teach me about the software side, which really just means replacing the table ballscrews and building better stepper mountings.

However, one other thing I really wanted to take care of was that idiotic column pivot mount that the older versions of these machines had.

https://docsmachine.com/cnc/images/G8689-76.jpg

I know LittleMachineShop has "solid column" conversion kits, but those are $500 plus shipping, and that's more than I wanted to put into this kind of a free-trade deal. So, for closer to $70 in steel and a fair days work, I came up with this:

https://docsmachine.com/cnc/images/G8689-92.jpg

Almost sixty pounds of 1/2" steel plate, bolted to both the base and the column including the column pivot bolt. Probably overkill, but I'm not an engineer. I just keep adding mass 'til stuff stops breaking. :D

Yes, when it comes time to tram the thing, I suspect it'll be rather time consuming to get everything shimmed just right, but then again, I also suspect that once properly trammed, it'll stay that way.

Doc.

ulav8r
03-31-2019, 12:46 AM
Add a couple of tabs to that base with threaded holes and a bolt bearing against the column to allow tilting and adjust tram. With the bolts snugged up against each side of the column, it should hold tram quite well.

Doc Nickel
03-31-2019, 02:14 AM
I'd considered several ways to "build in" adjustments, but I didn't like the idea of having such a beefy structure, and then only having it contact the column through the ends of a couple of setscrews.

Tramming the X axis will be easy- loosen the big nut and the four bolts. The bolts are in short slots, giving about 50 thou of travel left and right, which should be enough to fine tune. (And if not, I can open the slots up a bit.)

The Y axis will be a bit more involved, but again, will basically boil down to adding thin shims to either the lower big bolt or the upper pattern of bolts. Theoretically I can shim under the base casting feet as well.

Like I said, it'll likely be a little on the time-consuming side to do, but once it's done, it should stay done.

Doc.

junkaddict
03-31-2019, 02:23 AM
Nice. I bet that stiffens it way up.

darryl
03-31-2019, 02:49 AM
If you've gone that far you might as well add two pieces of rectangular tubing underneath, front to back, and inline with the mill base mounting holes. You might actually tap holes for the base mounting right into these pieces for easy assembly of the sandwich. I think a couple pieces of 2 x 2 x 1/4 wall tubing would help those 2 rear gussets do their job even better. Basically they are gussets underneath. It'll stiffen that flex point between the mill base and the upright on your base. Plus it gives a place for the mill base mounting bolts to go down into and be out of the way. Make these pieces 4 inches shorter than the base is deep to allow for another piece of the tubing across the front and one across the back. This restores the stability and gives you a place to mount adjustable feet right out at the corners.

Adding this square tubing frame underneath also gives you a way to adjust the angle between the base and the upright if it isn't close enough to 90. Place a shim over each tapped hole before mounting the mill base and assembling the sandwich. Then you will have a slight gap between the frame and your base at the back. You have the option to either spread that gap with a shim, or suck the gap smaller- with the effect of tilting the upright slightly- before you weld the frame to the base.

Doc Nickel
03-31-2019, 03:30 AM
I'd considered some bracing underneath the base plate, but I suspect that would be of very little additional benefit. Keeping in mind that that's 1/2" plate and almost 14" wide- we're already looking at some pretty heavy overkill, considering both the column and base castings are only 1/4" wall on average. And of likely no better than medicore quality cast iron, too.

This machine is likely not capable of producing enough force- even in a particularly energetic crash- to significantly flex that baseplate. :D

Doc.

tyrone shewlaces
03-31-2019, 03:58 AM
Cool. My baby Taig has the same pivot thing which I'll never, ever use. I was thinking of doing something similar but realized mine's so small that making it more rigid is like pushing a rope :D
A couple other similar constructions have crossed my mind too but I got to wondering if the various stresses inside the metal and from the welding will make things drift over time. That wouldn't be a big deal depending... (on that one you could just do some shimming again if necessary). But I could also just as likely be simply paranoid too as I don't know if things would ever move anyway.

Doc Nickel
03-31-2019, 04:29 AM
If anyone is interested in more of the details of this CNC rework, I have it up in my Projects Pages (http://docsmachine.com/cnc/minimill/grizzly01.html).

If nothing else, the part where I mill an internal bearing recess using a Woodruff key cutter was, I thought, pretty clever. :D

Doc.

metalfixer
03-31-2019, 06:10 AM
Checked out your Projects Page, very nice work.
While you have things apart, might want to think
about oil grooves.
https://www.cnczone.com/forums/benchtop-machines/376130-forum-2.html
I used an oil gun with way oil and regular 6mm grease fittings.

Larry

Doc Nickel
03-31-2019, 02:43 PM
Yep, I was going to do exactly that once the drive parts are done.

I've been curious, however, how people lube their ballscrews/ballnuts. Neither of mine (on the mill or the lathe) appear to have anything like an "oil port"- any holes in the housing have a setscrew in them. Are those screws there to actually retain something, or are those in fact oil ports that have simply been blocked and you're supposed to remove whichever one's convenient to access an oil passage?

Or do you just drip oil on the outside of the screw and let ti work it's way in?

Or do you just not lube ballscrews?

Doc.

tyrone shewlaces
03-31-2019, 05:15 PM
My cheapies have a threaded oiler hole in them. Two of the three even came with zerks - woohoo!
If it don't have 'em already, I dunno what to advise.
Oil hole is the one on the curved part of the flange. There are two other holes opposed to each other in the center of the flat part of the flange. I think those are for retaining the plastic wiper thing in place.

https://i.ebayimg.com/images/g/6ygAAOSwfeZcbD~P/s-l1600.jpg

smithdoor
03-31-2019, 06:08 PM
Looks great
I do not know why Grizzly and Harbor Freight could not add a few pounds of iron to there machine tools.
It would a big upgrade for there machine tools. Most of the tools I have purchased need work

Dave


Buddy of mine has a Grizzly G8689 desktop mill, that a previous owner had converted to CNC, but had cut a few corners. (I've mentioned it here a few times already :D )

I'm rebuilding the mechanical side in exchange for his helping teach me about the software side, which really just means replacing the table ballscrews and building better stepper mountings.

However, one other thing I really wanted to take care of was that idiotic column pivot mount that the older versions of these machines had.

https://docsmachine.com/cnc/images/G8689-76.jpg

I know LittleMachineShop has "solid column" conversion kits, but those are $500 plus shipping, and that's more than I wanted to put into this kind of a free-trade deal. So, for closer to $70 in steel and a fair days work, I came up with this:

https://docsmachine.com/cnc/images/G8689-92.jpg

Almost sixty pounds of 1/2" steel plate, bolted to both the base and the column including the column pivot bolt. Probably overkill, but I'm not an engineer. I just keep adding mass 'til stuff stops breaking. :D

Yes, when it comes time to tram the thing, I suspect it'll be rather time consuming to get everything shimmed just right, but then again, I also suspect that once properly trammed, it'll stay that way.

Doc.

metalfixer
03-31-2019, 06:18 PM
<<<< Or do you just drip oil on the outside of the screw and let it work it's way in?>>>>

I just squirt some way oil on the ballscrews, seems to work O.K.
Larry

Doc Nickel
04-01-2019, 03:25 PM
Upon reinspection, yes, mine have that threaded hole in the flange, too. Unfortunately, that doesn't help, as both are basically inaccessible when installed and in use, so I guess I'll just drizzle a little oil directly on the screws.

Doc.

Doozer
04-01-2019, 03:39 PM
Doc-
Your mount is about a million times better than the factory mount.
How did they sell such a piece of scrap?
Probably to get the user to buy the upgrade kit.
Marketing genius? Oh how I loathe marketing people.

-Doozer

danlb
04-01-2019, 04:03 PM
They most likely sold such a piece of scrap because most folks felt that it was better than the round column Rong Fu models. When the mini mill was one of the few bench top models available, they were considered quite a step up from an RF25.

Why did they not make it a little heavier and sturdier? Who knows! I suspect that it matched whatever they copied it from. An alternative idea is that it only needs to be stiff enough for the ratings. It was only rated for using a 1/2 inch end mill or drill, and 1 inch face mill. If you use anything bigger than that you should expect problems.

Dan

Wheels17
04-01-2019, 04:24 PM
Doc, I think you missed the point of ul8vr's post. The tabs aren't for holding tram, they're for adjusting before you tighten the "big bolts". I have a G0704, and I added the suggested tabs for tramming the head relative to the column. They reduced the time to tram by about 90%.

RB211
04-01-2019, 05:27 PM
Grizzly has nothing to do with the design of the cheapies they import from the likes of Sieg. I don't believe Sieg has engineers, nor a sound understanding of proper machine tool design.