Round Column Mill Conversion.

[Willyb]

Hi Guys

I am converting a round column bench mill to CNC and would like to get you opinions and help on my design.

Here is a list of the items I have to use on my Mill conversion.
Servo Motors driving Ball Screws through a 2:1 belt drive controlled with 320 Gecko drives. Software will be Mach3 with a remote pendent and a Manual Pulse Wheel to control both jogging and program speed. Replacing original Spindle Motor with a 1-1/2 to 2 hp, 3 phase unit controlled with a VFD. Maximum spindle rpm of no more than 4K. Full flow coolant in a totally enclosed cabinet. Hope I didn't miss anything.

Someday I would like to add a tool changer. I am not sure how well it would work with the R8 spindle, but I have seen it done. Anyhow, this is way down the road.

First of all, the 5 inches of Quill travel is just un-exceptable for the Z axis travel especially when tool changing. What I am planning to do is replace the round column with a built up structure out of 1/2" steel plate welded together. This new column will be bolted to the mills base but moved back one inch to give extra travel on the Y axis. I am also planning to mount a set of Linear Rails onto the front side of this new column for the Z axis. A new Spindle head will be made to hold the spindle and be mounted to the Linear Bearings. The spindle head will be controlled with a ball screw.

One of my first questions is what to do about the spindle cartridge?? The original one is an R8 unit and draw bar with a single set of greased taper roller bearings. Nothing fancy. I would really like to change it to something with a flange or possibly a square body for mounting and a better set of bearings but the cost would likely be more than I paid for the complete mill. Any ideas what to do about the spindle or who might have a suitable replacement at a reasonable cost? When all said and done, I will likely end up remounting the original spindle and hope for the best.

A counter balance weight will be mounted inside the column with some rollers and chain connected to the spindle head. This should get away from having to have any fancy brakes on the ball screw/servo motor to prevent the spindle from crashing into the table when the power is turned off.

The original 1-1/2 hp single phase motor will be replaced with a 3 phase unit and a VFD for control. The spindle will be belt driven with a two step pulley arrangement for a couple of speed options.

Let me know what you think of my design (good and bad) Also interested in any change or modifications that you think would be a good idea.

Bill

[wizard]

Well the first thing that I have to think about is why didn't you just purchase a square column mill with dovetails? I also suspect that you are underestimating how difficult this conversion will be, atleast as you describe the column replacement.

As to the motor drive the VFD is a nice idea but you failed to describe intended usage. You may very well still have a need for more than two ratios on the pullies. Frankly I'd suggest simply reusing the current pullies and finding the correct length belt.

In any event it isn't worth commenting on the rest of your posting as I'm really bothered by the weldment description you made.

Dave

[Willyb]

The reason why I am converting this mill is because I happen to have a new one sitting in my shop. To have a square column mill shipped to Canada would cost more than $1,000.00 US.

Yes, life would be nice to do everything the easy way. I have built many mechanical machines in my life and I am not about to let this one scare me.

Willyb

[motomitch1]

Hi Willyb,

Heres some pictures of my 300 dollar round column converted to square column. It wasn't that hard but it did take a lot of time. I tried to put the pictures in order but it didn't work out that way.

http://www.sickrcs.com/new_page_1.htm

[ViperTX]

motomitch1....how much of the ballscrew was sticking out the back end of your lathe when you machines the ends? Any problem with whipping (how did you support the end?)...what RPM did you use?

Thanks and looks like a nice job!

[miljnor]

i used about 800rpm on my ballscrews and took realy little cuts. on the longest ballscrew 42" (most of which was sticking out) I used a piece of wood clamped to a vise with a hole in it for the whipping (which realy wasn't much but better safe then sorry). I trashed a few inserts doing it but they were the cheap HF style and needed getting rid of anyway.

I think the speed can be played with quit abit but its hard to tell as I only did one at home and the interupted cut on a HF 9x7 lathe with cheap inserts aint a good combo!

just check out your sight Moto and that rc truck is awsome. You should put it in a post and tell us what you made ect... The head on the motor is a nice touch with the finns cut at an angle. Very nice!

[Willyb]

Hi Motomitch1

Thanks for putting the pictures of your round column cnc mill conversion up. It looks great. This is the same idea as what I am going to do. Glad to see that someone else wasn't afraid to try this. What was the hardest part of the whole conversion? Any problems squaring up the column? Thanks again for the pictures.

Willyb

[miljnor]

motomitch inspired me as well his square column conversion is awsome!

here is the link to mine although he took way more pictures than me the conversion is very similar.

http://www.cnczone.com/forums/showthread.php?t=9383

how is yours working motomitch1??? still going strong? and would you change anything? as I am not as far along (still time for some changes).

[miljnor]

Hi Michael Great job on your round column mill conversion. Thanks for putting the pictures up. They help allot. If you have anymore I would love to see them. Do you have a web site? I am starting on my round column mill in the near future and I am just trying to get some ideas of the best way to go about it. I have been looking at that round column of this mill for along time trying to figure out what to do with it. The limit of 5 inches of Quill for Z travel is just un-exceptable, especially when trying to change tooling. I knew what I wanted to do with it but everyone told me that I was nuts to try it. Now that I see other guys doing it, (like you) I don't feel as bad to give it a try. I have some questions which I hope you don't mined me asking about your conversion. (1) What size is the vertical tube that you used for the replacement column? (2) I see you welded some bars onto the front edge for mounting the linear rails. Did you have any problems with these warping anything after welding? (3) What did you have to do to true everything up after welding? I am limited to what I can machine and the column would be to large. I guess I could take it to a machine shop to get it trued up if needed. (4) What size are your linear rails? They look massive. Wow, six bolts per bearing. (5) What are you planning to use for a spindle motor? (6) Do you have a good place to get replacement bearings for these spindles? (7) What are your thoughts on trying to keep the coolant out of the lower spindle bearing of these cheaper spindles? I don't think my spindle even has a proper seal in it down there. I think it has a rubber washer that screws into the bottom of the spindle body? And I am planning to put the mill in a fully enclosed cabinet and use full flow coolant. So there is going to be lots of coolant flying all over the place. What about making some kind of aluminum adapter that would fit onto the bottom of the spindle that you could put air pressure to for a positive pressure to keep the coolant out. Something like what the big boys do on their spindles? A type of air purge? Any thoughts on this? I have lots of other questions, but I will wait for another day. I have ask to many questions now. I really appreciate all your help with my questions. Thanks. Talk to you later. Bill Blackburn Also known as Willyb

1. The tube I used was just laying around and measured 6x3" with 1/2" wall thickness I dont have the length on me but the travel on the slides will be just over 21"

2. the base plate and the top plate are machined before welding. then while welding you make damn sure to sqare everything up and tack it together and check it again. (I think the stress got to me here because I must have check the thing about 20-30 times before finale weld ) After welding I let the thing sit in the sun outside for a couple of weeks for some heat cycles (a heat treatment would do the same thing, better but, I was being cheap) Then I put two kurt style vises in my VF-2 and machined the Rail pads being sure to true the column BEFORE MACHINING to the Base. This column was so thick I doubt seriously if the warpage was all that serious to begine with.

3&4. I have a machineshop so in effect I cheated with professional machines. but I only had a vf-2 at the time and had to compromise on the length of the support pads. if you look at the picture you can see the rails hang off a little (the vf-2 only has 30" of travel) and the rails are IKO linears LRX25 (basically 1" wide rail) I actually was looking for the next size down but those were almost 2 times the price do to availablity.

5. the spindle motor is a 2.5hp continuous duty treadmill motor wich is massive. I have pictures but they will have to wait till this weekend to get posted as I cant find the charger and dont have time to look for it (just moved)

6. Any bearing house should be able to help you. The ones I listed previously in this thread are some of the best on the market. The Nipponees rate their bearings lower than abec specs so you can get them to perform at the next higher Abec standard than rated. (i am tired hope that makes sense).

7. Hadn't realy though of an air purge that actually might be a good Idea. I was going to make an oil seal similar to an oil seal on the crankshaft of a car but probably a double seal insted of single. Will give some serious thoughts on the air thingy though! glad you mentioned it.

[Willyb]

Hi Michael

Thanks for the help with my questions. And the pictures are great. They have helped allot.

Willyb

[miljnor]

no problem man. will have some more pictures up after the camera charges up. maybe by tonight. And you can still use the email thing. I just thought since the questions were zone related It would be cool for everyone to see and comment. God knows I do some stupid sh!t from time to time and always nice for someone here to point it out, so it can be fixed.

[Willyb]

Here is the Mill that I will be converting. Hope to get started fairly soon. I am going to start a new thread once I start and will post pictures as I go.

Willyb