# Rebuilding mill



## Grimm (Oct 5, 2009)

I purchased a mini mill in 2009 and have liked it a lot, but I wanted to update it a bit and add a rotary table, etc. In the process I though that I might as well just rebuild the whole thing and add a column brace and cheap DRO as well. I have started the rebuild and everything is going ok so far. I messed up on the column brace, but I think I can fix it. This weekend I tore apart the mill head and lapped all of the surfaces and gib. I wanted to re-align the head with the column and make sure that they are parallel to each other. The only rod I have, that I also had a collet for, was a 8" length of 3/8" brass rod. I also have a collection of rods from old printers, but they are all of different sizes then the collets I have.







Is the brass rod ok for this kind of test? I set up the column so it was horizontal (I put it in my vice), then I put the head back together but only tightened one of the bolts and left the other three tight but not fully tightened. I then set up my test indicator to measure the side of the brass bar and attached the magnetic base to the column. I then adjusted the head gib and zeroed the indicator. I used a rubber mallot on the draw bar to do very small adjustments to the lateral alignment (x axis?) as I ran the head up and down the column, resetting the indicator after every adjustment. I was able to get it down to less then .001 (.0003+- maybe?) over 6 inches of the bar. I'm hoping that this means the bar is strait and ok for this test? Once I had it as good as I thought I could get it I carefully took the head off and tightened all of the bolts down and then put it back on the column and retested it. It was very close to what I had before, maybe a bit more off but not more then .001" (the needle bounced around about +-.0004in. during the test). The y axis alignment worried me the most as there is no way to make any adjustment short of putting shims in. I had cleaned and lapped all of the surfaces so I was hoping it would be good. I set up the indicator to measure the top of the bar and again attached the magnetic base to the column. Over 6 inches of the bar I got about a .0008 inch change in the indicator. Is this ok? Should I worry too much about it and try to shim the head? Thanks, I guess what I'm hoping to get out of all this is a better more tight machine. Jason


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## Grimm (Oct 5, 2009)

No comments on what I have done so far? I guess that means that I'm either doing it right or very, very wrong. Knowing my luck, it's most likely the latter.









I have given this a lot of thought and had many 'Doh' moments. One of those moments was when I realized that I could spin the spindle and see how concentric the rod was. It wasn't very straight at all, but I was able to bend it gently back to be concentric with the spindle. I was able to get the head lined up with the column to within 0.01 inches. It also turned out that the head nodded towards the column by more then 0.04 inches. I added a 0.02 shim to see if that would line it up better. I didn't want to add more then that because I was measuring from the end of the bar which was, if you add in the length of the head, over 10 inches in length. The head is about 4 inches long so I thought 0.02 inch shim would work. 


Here is a picture of the measurement set up. 












Here is some pictures of the construction of the column brace:


I'm using a 1/4" hot-rolled plate that is 4" wide by 12" long. The first picture is of the layout for the screw holes. The mistake I made here was the position of the large hole for the main attachment screw for the column. It should have been placed 1/4" over because the column is not centered there. I ended up having to hand file the hole to move it over a bit, luckily it worked. 












The next image is milling out the large hole with my shiny new rotary table. I purchased the rotary table from the Little Machine Shop( 1810 http://www.littlemachineshop.com/products/product_view.php?ProductID=1810&category=1034788869 ) and I really like it. It is much better then the one I first purchased from Grizzly, the H5940, which I had to return. I also did all of this work before I tore down the mill, as I wouldn't have been able to do this with out the mill anyway.



















This picture is of the brace finally installed on the column.











I mounted the column back onto the mill base and the head too so I could tram the mill before drilling the final two holes into the base for the brace. I used my lathe faceplate to tram the mill it appeared to work fine for the job. I just finger tightened the screws holding the faceplate down so I wouldn't warp it. I was able to get the x-axis to tram no problem.











I drilled and tapped the two holes and here is a picture of the results. 










The two screws on the out side pull the column back and the two middle ones push the column forward. I like this design because, not only does it keep the column more rigid, it allows you to tram the y-axis as well. 


Now comes the next problem, I wasn't able to tram the y-axis at all. I have a 0.04" tilt that I can not get rid of with the column brace adjustment. Every adjustment I try just moves the error but doesn't fix it. I think this means that the head is not parallel with the column. The next step is I'm going to remove the shim and see what that does and if it gets worse, I will try a thicker shim. Once I get this worked out then I will start on drilling holes for the z-axis DRO. Yay!









Jason


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## Grimm (Oct 5, 2009)

Today was very productive.







I first checked the head alignment without the shim, and I was able to tram the y-axis, go figure. I don't know what I did right or wrong, but I was able to get it below 0.01 inch. I guess we will see how good a cut looks once I have everything back together. 

I also finished attaching the Igaging DROs I purchased from Grizzly. Reading all the forum postings on these and seeing pictures of how others had set up theirs, I put together a short list of things I wanted to try and avoid when I did mine. 

1) Protect them as best I can.
2) Preserve as much of the y-axis travel as I can.
3) Don't put them in places that will limit future upgrades to the mill.

The z-axis didn't appear to be much of an issue so I just concentrated on the x and y axis. Many people placed the x-axis reader right in the center, this looses a lot of y-axis travel especially when you add in the rear way cover. I did see one guy off-set his y-axis reader and thought that would be a perfect method to get it out of the way. He didn't do the same for his x-axis which I thought was strange, given how well it worked for the y-axis. So I built a bracket that holds both of the x and y axis readers and connects to the mill's saddle. This way both readers are off-set and out of the way.


On to the pictures:

Here is an overview of the DROs.










Here is a close-up of the z-axis reader. I used one of the brackets that came with the DRO to attach it to the mill head. I just straitened it out until it had the correct hight using my vice. I'm adding a air spring to the mill and removing the old torsion spring. This gives me a lot of room to attach the DRO, options are much more limited with the torsion spring. Although several people have found good solutions. I wanted the longer travel with the air spring so it worked out well.











The next image is of the x-axis DRO, you can see that by off-setting the reader, the end of the DRO bar sticks out off the end of the table by 2.5 inches. One of the compromises by doing the offset. It still allows me to add an x-axis power feed attachment at a later date, which would in turn also help to protect the bar.











This image is of the y-axis DRO and it's reader nicely tucked under the table and out of the way. The offset allows the end of the DRO bar to be flush with the front of the mill base.











Here is a picture of the DRO bracket which holds both the x and y-axis readers and attaches to the mill saddle. 











This image shows the y-axis travel as far back as it can go with the DRO installed. I loose about .25 inches in travel, a little more with the rear way cover installed. I'm thinking that a travel stop might be a good idea so I don't accidentally mash the DRO bar in to the column brace. 











Here is an overhead view of the table in that same position:










I'm a bit worried about protecting the x-axis DRO but I haven't seen or thought of a good way of doing it.







If I keep it clean it might be ok? 

Next is the air spring.

Jason


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## Grimm (Oct 5, 2009)

The air-spring is installed (also purchased from LMS)!







The only thing I had to modify was the screw that attaches the air-spring to the column. Because I added the extra column brace it made the column thicker and the screw that came with the kit is now too short. I purchased a longer version (300mm) of the screw and used that instead of the supplied one. There was still a problem, the longer screw would not fit inside the column at an angle where I could get it to slide into the hole I drilled for it. So I cut off a bit on the end of the screw with a Dremel cut-off wheel. I took off about 1/4" and then I was able to squeak it in to the hole and still had enough threads to bolt it securely on the outside of the column. 






















I finished putting the mill back together and setting up the DRO displays. For the DRO displays all I did was to screw a bit of 20-gauge steel I had to the wall next to the mill and attach the displays to it. They are magnetic so it's real easy and so far they are easy to see and use. 












I did some test cuts with a 3/16" end mill on 360 brass and 1018 steel. I took off .02 each pass and didn't have any chatter or complaints from the mill. It was smooth as silk.







Happy Jason, now on to a real project and give the mill a better workout.


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## Semper Vaporo (Jan 2, 2008)

Thank you for posting this. I have considered doing the same with my mill. Do you have a photo of the rear chip guard and the DRO bar? I am wondering if the chip guard goes over the bar or under it.

There are two reasons I have hesitated to do this to mine (well, maybe 3, considering my hamhanded abilities, I am doubtful if I could get the bolt holes in the correct places!) 

One is that my mill was so well aligned from the factory that I fear I will not get it back to acceptable limits. 

The other is that I have digital readouts on my Lathe and I have had way too many problems with them to make them worthwhile. 1) They are battery operated and the batteries last almost long enough to actually make one part. 2) The mechanicals that do the reading get full of chips and soon do not register motion (nothing like turning the crank handle and not seeing any change in the display!). 3) Somehow swarf has managed to get between the glued down plastic cover over the display (two levels of plastic!) and the Liquid Crystal Display... I doubt if I'll ever understand how a brass chip got there!)

So... are the readouts battery operated or is there an AC adapter for the power?

I am glad to see your display readouts mounted up out of the way, so maybe the swarf won't get between the display and the cover so easily, but I still worry about swarf getting into the space between the sensors and the slider bars along side and below the table. I realize you have not used it enough to make a mountain of swarf, but do you have any feel for what happens if swarf gets into that space? Do you have any method of keeping it out? (Some sort of scraper or brush that knocks it off so it won't get in as the bar passes through the sensor, or the sensor passes over the bar?)


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## Grimm (Oct 5, 2009)

I understand your hesitation, I had the same reservations. The guard goes under the DRO bar, at least on my mill as it attaches to the saddle. 











I tried to think of a good way to add a cover for it but it's difficult because the only place to attach it to is the table. At this time I have decided to not have a cover for the bar because I'm more worried about the swarf getting packed in under it and really messing with the DRO. At least without a cover I can get in there and clean it out easily and often. Time will tell if swarf is going to get into the reader and cause it to fail. 


No worries about hamhanded issues, if my hamhandedness didn't kill my mill, you will probably do much better then me.









The DROs I purchased from Grizzly and are made by Igaging. Here is a link to the 6-inch one: http://www.grizzly.com/products/0-6-Digital-Fractional-Horizontal-Vertical-Remote-Scale/T21577 They are battery powered, and the batteries go into the display. You might be able to get a Shumatec display to work with the readers, but I'm not sure. 


I went with these because I have seen some good reviews on other boards about them. One fellow said he has been using them for over a year and still has not had to change the batteries yet. They come with two sets of batteries (CR2032) in the box which is cool. I will let everyone know when I have to change them out. I don't know if you can tell from the pictures but the reader completely surrounds the bar and has a pretty tight fit. Although probably not tight enough to keep out the swarf? If it becomes a problem I will have to devise some kind of wiper or brush.


Jason


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## spincaster (Mar 10, 2012)

why not convert to cnc?


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## Grimm (Oct 5, 2009)

I would love to go CNC, I just don't have the $ to do it.







That and I already feel that I'm over my head with just learning the manual mill and lathe stuff.







I just might save my $ and get one of the CNC ready Sherline machines at some point, they appear to be in my price range. Maybe they will sell me one with out the linux box, as I already run linux at home and work. 

Jason


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## Dwight Ennis (Jan 2, 2008)

I'm a bit worried about protecting the x-axis DRO but I haven't seen or thought of a good way of doing it. Could you make a thin sheet metal (brass?) U-section that fits down over the DRO (with clearance of course) and mounts to the front of the column? That chould keep chips and oil out of it.


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## spincaster (Mar 10, 2012)

Posted By Grimm on 08 Apr 2012 10:10 PM 
I would love to go CNC, I just don't have the $ to do it. 







  That and I already feel that I'm over my head with just learning the manual mill and lathe stuff. 







  I just might save my $ and get one of the CNC ready Sherline machines at some point, they appear to be in my price range.  Maybe they will sell me one with out the linux box, as I already run linux at home and work.  
 
Jason


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## Grimm (Oct 5, 2009)

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I was thinking of putting on a simple flange over the DRO to help shield it but I don't know how much good it will do. And swarf will still build up and get caught under it because of the way protector. I'm just thinking that I'm going to just have to keep it clean and make sure I don't allow a lot of swarf to build up. 

Jason


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## Dwight Ennis (Jan 2, 2008)

Oh well, it was a thought.







BTW, you can definitely get a Sherline CNC machine sans computer. The only rub is that the stepper controller and its associated power supply (which also supplies the stepper motors) is mounted in the bottom of the linux box. Talk to them and see what can be done. I've found them to be quite accommodating.


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## Semper Vaporo (Jan 2, 2008)

I was thinking of something like this:










The gray is a stiff cloth (like oil cloth?) that can crush as the mill table moves toward the post. The yellow bar is a stiff steel/aluminium/brass bar that just rests on the front of the upright/post and is free to slide on it as the mill table moves left and right. The bent wire at each end is just springy enough to help the oil cloth expand as the table moves away from the post. The digital sensor head slides under the cloth as the table moves left and right. The cloth is attached to the back surface (not on top) of the mill table (probably behind another bar for support and strength of attachment).

I realize a heavy chip load might cause the whole thing to tip to one side and dump the load and possibly interfere with the movement of the table, but I think it would be easier to keep the cloth surface clear of chips more so that trying to keep the slider bar clean. And just one chip in the wrong spot while the table is in motion could get into the sensor area unnoticed.


I have been thinking of doing something like this on my mill because the accordian pleated shield is a wee bit narrow and chips still get under it and into the ways of the base.


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## Grimm (Oct 5, 2009)

Semper, that is a very interesting idea! If you can get some cloth that is stiff enough diagonally, you might be able to anchor it down on the column side. Attach it to the same spot that the original protector is attached with a ball-bearing race or some other contraption to keep it aligned with the table. You could even make it as wide as the table. It also has the possibility to give you even more y-axis movement by removing the original way protector. Very interesting, thanks.

Jason 
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