What are the most cost-effective modifications to a Grizz or HF mini-mill?

knudsen said:
These are about the same thing as your Z DRO, Joe, but they fit the cheap part of the bill:

http://www.amazon.com/iGaging-DigiMAG-Magnetic-Digital-Readout/dp/B003JUII2A

As you can see, Quint Graphics sells them on Amazon. They have different lengths. Grizzly sells one or two sizes. Info: http://www.igaging.com/page97.html Well, not much info.

I searched and searched and finally found someone who used them on a mill. Guy said they were pretty good, but kept going to sleep and was annoying. These cost about the same as a long digital caliper on sale at HF, so I was going to go for it, then bought a knee mill. I did make a Z axis from a cheap caliper before I knew of these, and it worked OK, but as soon as I added the Z counter weight, so Z axis didn't totally suck, I found I was just reading the dial instead of the DRO. I never put it back on after belt conversion.
Click to expand...


These are the ones I installed (3) and really like them.

Also installed the air spring kit from Little Machine Shop and it has been well worth it IMO.
 
The only mod I have done up to this point was to add the air spring kit from LittleMachineShop (with the longer rack). The longer rack has helped out with a couple of projects already and there is no more head drop thanks to the air spring kit.
My next mod will be the belt drive but at the speed I work that may be a while.

Randy
 
From the list, I'd say a QC collet system or cheap DRO's if you plan on staying with the cheap ones. If you plan to upgrade in the future I wouldn't waste time mounting the cheap ones now, I'd move on to something else and wait.
 
110octane said:
Everyone who has one of these "mill-drills" or buys one (fitted with R8 or other collet system with a draw bar), be sure and check the draw bar out. I had an ENCO in the '90's with R8 collet spindle and the 7/16-20 draw bar. After using the machine for about six months, I tightened a collet holding an end mill. I felt the bolt turn just a "little" bit weird, but I thought (Dah!) that the collet had just pulled up on the taper. After a few passes the collet dropped out of the spindle with no warning and went by me across the shop. I was lucky.

Examination showed that the draw bar was two piece with the hex nut fixed to the bar with a solid (tapered?) pin. The assembly had been blued or surface treated and the ends of the pin were virtually impossible to see without very careful study. The "slip" I felt was the pin beginning to shear. I immediately turned up a solid draw bar on my trusty Logan 10" lathe. Don't let this happen to you, that thing could have really hurt!

I sold the mill-drill in 2000 (Y2K!) and bought a Grizzly knee mill. This is a step up and at that time the price was right. It is a 9 X 42 (I think) and the head will rotate but not swivel. I really like this machine. Needless to say the first thing I did before I pulled up any tooling in the spindle was to check the draw bar - yes, it is one piece. Be safe, Geoff
Click to expand...

My Micro-Mark mini mill came with a draw bar that engaged about 1/4" of threads on the drill spindle, and only about 3 threads on the collet spindle. After using it for about a week, the bottom most threads on the draw bar broke loose. Fortunately this happened when I was installing the spindle, and not under power.

I went to the hardware store to buy a long 7/16 fine thread bolt, but wasn't able to find one. So I bought an even longer coarse thread one, cut off the threaded portion, and threaded it 7/16-20. Although the new draw bar is only a grade 5 bolt, it engages about 1/2 inch of threads. So far it's working well. Is the bolt strength going to be adequate?

Walt
 
Walt said:
My Micro-Mark mini mill came with a draw bar that engaged about 1/4" of threads on the drill spindle, and only about 3 threads on the collet spindle. After using it for about a week, the bottom most threads on the draw bar broke loose. Fortunately this happened when I was installing the spindle, and not under power.

I went to the hardware store to buy a long 7/16 fine thread bolt, but wasn't able to find one. So I bought an even longer coarse thread one, cut off the threaded portion, and threaded it 7/16-20. Although the new draw bar is only a grade 5 bolt, it engages about 1/2 inch of threads. So far it's working well. Is the bolt strength going to be adequate?

Walt
Click to expand...

The strength isn't that important as the drawbar doesn't hold the collet in place, the taper does, and the drawbar just has to hold the collet into engagement with the taper.
The length of thread engagement matters more, as the greater the engagement the more the load is spread over the threads, both when drawing the collet into place and also when tapping on it to break the taper.

I had to make one for my Sieg X1 as the one that came with it is metric and my collets are 3/8-16.
I used a length of 'all thread' and welded a coupling nut to the top, then reduced the bottom of the nut to engage with the spindle collar.

'All thread' is probably grade 5 at best, but I have plenty of thread engagement and there's no distortion of either the drawbar threads or of those in the collets.


M
 
My 2nd hand HF X2 came with scales (minus read out), and a belt drive made by the previous owner. I added a Shumatec DRO-550, the air spring and rack kit from LMS, a larger 2 1/2 hp treadmill motor and controller, and a home brew X axis power feed. The most cost effective was the self assembled DRO-550, and the treadmill motor and controller. Though I did purchase the parts to repair the origional controller, never got around to it.

Chuck
 
Nelson said:
A question to those of you who own mini-mills.
Which are the most cost-effective modifications that you can make to a HF or Grizzly Mini-mill?...............
.......................................Let us know what is on your list of TOP modifications!

Best,

Nelson
Click to expand...

CNC by a mile!

1: It's a fun project.

2: It removes the tedium of turning handles.

3: You can do machining that is literally impossible to do by hand.

4: It increases the versatility of your machine, i.e. cut out an instrument panel, change to an engraving bit and engrave the instrument panel, put a Sharpie in the chuck and make a poster, change the bit again and make a three dimensional portrait in wood, plastic or metal, add a fourth axis and build a Mars Lander....well, not quite but you get the idea.


M
 
I concur that most of the all thread rod is probably in the neighborhood of grade 5. It seems to be rather "soft" since it is going to be a very ductile because the threads are rolled and not cut. Today, most all bolts are made by rolling. The R8 taper is not a self retaining taper because the included angle is too steep. I think that the all thread should hold the R8 in place. The connection of the all thread to whatever nut is attached is most likely the weakest point. Welding undercut should be avoided for example.
I turned the one I used for a replacement from 1018 or 1045, I can't recall. I used a follower rest to keep the long rod on center. There are replacement drawbars sold for Bridgeport machines and if, long enough, could be adapted to a mini-mill provided that cost is not prohibitive.
Mainly, just work safe. In my case it was one of those defects that I failed to notice. In my defense it was extremely difficult to detect without knowing to look at the assembly. A bright light, a magnifying glass, and maybe even dye penetrant or mag particle would have been required to identify the defect.
Regards, Geoff Morgan
 
110octane said:
The connection of the all thread to whatever nut is attached is most likely the weakest point. Welding undercut should be avoided for example.
Click to expand...


Agreed, that's why I used an all-thread connector which is really just a very long nut. Big plug weld at the top of the connector down to the all-thread which is maybe 1/4" from the top, then turn the bottom of the connector in the lathe to a shoulder, which engages with the top of the spindle.
Total cost about $5 and I still have about 2' of all-thread left over.

If the weld failed to properly penetrate the top of the all-thread then the weld might fail when undoing the drawbar and the collet could still be released by tapping the remains of the drawbar with a punch; however it would never fail by being tightened, so there would be no danger of the collet being accidentally released during operation.

Also, I suppose you could harden the last inch or so of the drawbar thread that engages with the collet, but the collets are pretty hard and if either of the threads was to get damaged I'd rather it was on the easily replaced drawbar rather than the collet.


M
 
I have a set of Chinese R8 collets and I am not sure as to the method of manufacture. I suspect the whole unit was carburized to a shallow depth (maybe 0.06" to 0.08") and then ground on the taper and the shank. The threads do not seem to have been ground after heat treatment. What is strange is the collets seem to have been made from two pieces. Looking at the threaded end the top edge of the shank appears to have been rolled over a separate component that holds the threads. I have a couple of high quality US "Royal" brand R8 collets that are at least to a casual observation to be solid. I have not had any failures or separation of components with any of these collets, but I'm suspicious. I have never checked the runout on any of these collets either. You get what you pay for and in all honesty I have not had any problems with obtaining tolerances at least the ones I have worked to which are not to tenths.
I also have a collection of Chinese, British, and US 5C collets (as well as a few 3AT and 3C which are all US or Italy). The Chinese collets vary a lot in runout. The best I can get is within about 0.001" runout with the Chinese collets. However a number of them can produce a little more than 0.003". The lesson to this is to check for accuracy before you undertake a close tolerance project. You might end up blaming yourself when things don't measure up and all the time it was a work holding matter. I understand that top notch machinists (at least those of the last recent generation) use a new collet and grind the collet in the spindle to assure a precision runout. I think this was SOP in grinding lathes including grinding the centers anytime the centers were changed.
I don't have to worry about those kind of tolerances. If I get any less than 0.001" runout in my turning work, I consider it a miracle. After adjusting the tailstock on my lathe, I have been able to turn between centers, flip the work and get just a "shadow" of lap which I guess represents about 0.0005" T.I.R.which I also consider a matter of luck rather that skill.
Geoff Morgan
 
You must log in or register to reply here.
Back
Top