Another X2 CNC Conversion (yay!)

[skmetal7]

I think I found what is binding, its the xy dovetail saddle. the base is fine as far as i can tell. I might take it to school and see if i can have it surface ground.

[skmetal7]

Happy New Years!!

Ok so it has been a while since i updated this thread, school and work get in the way

i have decided to go back to steppers and I plan to get them from Keling, along with drivers and PSU.

I just ordered my ballscrews from homeshopcnc.com, hopefully Ill get them soon. been reading about roton ballscrews and Im GLAD i stayed away from them (not meant for cnc applications), then I'll machine the ends for the ac bearings, and attempt to load them with larger balls.

I finished the x and y ballscrew mounts, now I have to work on the z axis. And then make the parts for the linear rails.

I started the part that holds the z ballnut, it is like Hoss' design but its three pieces and made out of aluminum. Just waiting for my thrust bearings from McMaster Carr. And have to make the plate that holds it all together. Waiting for pullies and belt from SDP/SI.

Whats the best place to get all the limit switches, wire, plugs for the stepper motors (like mic plugs), wire sleeving (either the ss type or the black carbon-fiber-like sleaving), I have looked at mouser and digi-key but I got lost

Pic 1 is the y axis ac bearing holder (with ac bearings)
pic 2 is the z axis ballnut mount
pic 3 is the y axis ballscrew mount being squared
pic 4 all square!
pic 5 all holes drilled
pic 6 completed assembly, minus stepper and stepper mount from ebay
pic 7 parting off the x axis ac bearing holder
pic 8 cutting x axis ballscrew mount (I need a bandsaw...)
pic 9 squared x axis mount (and really shinny)
pics 10,11 cad model

[blades]

skmetal7, I love your project! Nice job on everything. Was wondering why more people don't take advantage of mounting the motor on the left side of the table like you have. It looks like it would be a simpler installation. Haven't decided if I will mount mine there, or in front with a timing belt arrangement (although I already ordered my belts & pulleys).

I like your Z column design, however I'm concerned with the use of bearing slides. While they will be deadly accurate for linear positioning, they *may* cause chatter and vibration when you introduce the very cyclic/impact load of milling, because there's almost zero drag on them. The highest accuracy would come from linear slides, but the highest stability will come from dovetail slides, locked into position. Bearing slides are only offering you point contact along the hardened rails. If you want to use bearing slides, consider oversizing the slide units, which may help. I hate to see you spend good $$ on something that theoretically is a good design and should work, but in reality may not.

Don't lose sight of the fact that this is a $400 mill (at least mine was with the 20% off coupon ), and will never approach a Bridgeport in terms of ruggedness, or a Jig Bore in terms of accuracy.
That being said, I love seeing all the improvements that can be done to it. I took my HF 44991 completely apart and cleaned and deburred everything. I also saw the bind at the end of the table travel that you mentioned. If you adjust it so it doesn't bind up there, it gets too sloppy in the middle. This is an expected wear characteristic for an old mill, but not something you expect to see on a brand new machine.

[skmetal7]

Thanks blades!

Been working on this some more and have just about all of the mounts finished. Just finished the z axis earlier and was able to set a preload on the thrust bearings without needing to use shims (took a while though).

pic 1 is the z axis
pic 2 is the bore for the bearing
pic 3 turning the ballnut spindle, .100" DOC
pic 4 is the completed assembly

I recieved the ballscrews from homeshopcnc.com and they look great, very smooth. Ill have to get some larger balls to preload them, but first I have to figure out how much backlash they have. I attempted to turn one of them on my 8x12 and WOW they are HARD!! I got past the ball races and the lathe was still struggling..... Ill try and replace my aluminum QCTP and put on the old 4 way post and see if that helps. I am using carbide, but I'm not sure what the best way to center drill them is, my center drills can barley touch them (HSS). And how in the world am I gonna thread them????

[whoafat]

Blades,
I'm vicariously following SKs transformation of his Mini. I have some noobs questions regarding your comments. Can you please clarify what you mean by your concern of using bearing slides in the Z-column. Are you referring to the ballscrew-ballnut assembly? I am posing the above questions because I am in fact finding stage of my own CNC conversion,
thanks,
Wilfred

[blades]

Although I've had zero experience machining ball screws, they *SHOULD* only be case hardened, maybe .030 (give or take) case depth. Once you get past the case, it should machine nicely for you. Same on the ends where you're trying to center-drill, if you can get past the case somehow. In a pinch, you can use a carbide tipped masonary drill to break the case and get your center started.

Looks like you're using the same size belt & pulleys I'm using on mine. I started out with .080 pitch XML x .25 wide size belt & pulleys, but it just looked too small, so I jumped up to the .200 pitch x .375 wide belt & pulleys and it appears to be much more appropriately sized.

[blades]

Originally Posted by whoafat Blades, I'm vicariously following SKs transformation of his Mini. I have some noobs questions regarding your comments. Can you please clarify what you mean by your concern of using bearing slides in the Z-column. Are you referring to the ballscrew-ballnut assembly? I am posing the above questions because I am in fact finding stage of my own CNC conversion, thanks, Wilfred

Hey Wilfred,

No, no concern at all with the ballscrew assembly, just the bearing slides themselves. Without a means to lock the head into position solidly, the forces and vibration from milling are transfered to the ball slides, which only have multiple point contact between the slide rails and the X2's head.

Ball slides have exellent load-carrying and positioning characteristics when used on automation equipment, but are not the best at handling the type of load a milling cutter could potentially put on them. For example, the slides may work fine for cutting softer materials, or even steel with a smaller diameter end mill. But if you tried to cut steel (or some similarly hard material) with a larger cutter, you would definately see the effects of this.

Many years ago I tried using a ball slide assembly to machine with, and I remember getting all kinds of cutter chatter and vibration because of the ball slides. In fairness skmetal's design though, I only used one slide saddle, and not multiple ones like he has in his design. That would probably make a huge difference.

Sometimes when milling (regardless of material), it's beneficial to "ride the brakes" on the dovetail slides, something you can't do with ball slides. This not only improves surface finish, but helps reduce the vibration you would normally see due to slop in the machine ways (dovetails). The act of cranking the machine handle to traverse the table will naturally push the table from one side of the slop to the other with each turn of the handle.The bearing slides have almost no slop in them, but they are still capable of transfering vibration.

[whoafat]

Thanks Blade for taking the time to clarify matters,
Wilfred

[skmetal7]

yeah I am concerned with chatter also, so if it does chatter a lot I can always remove the slides and use the dovetail slide. The NSK linear slides have some preload and are pretty solid (I got them off ebay cheap so if it doesn't work I can always resell them). Its just that the dovetail has so much play and If I try to tighten it down at all it will bind.

On the belt size, I'm stealing Hoss' idea :P and using the same belt size. Yeah .080 x .25" is pretty tiny.

[blades]

It's entirely possible that you won't see any issues at all with the ball slides, because you are using multiple carriages, and the head has a good amount of heft to it, all working in your favor to reduce vibration. I see a lot of home-brew designs that use ball slides on the table as well. If it works for milling, it will allow for much improved accuracy and smoothness of table movement. Also very much simplifies design and construction, making them overall a very good bang-for-the-buck, as long as there's no vibration issues.

[skmetal7]

I was finally able to turn the end of the y axis ballscrew. Its hard even far after the ball race, but I was able to break through it. And the ends must have been work hardened when they cut them to length. In order to face off the end, I had to lock my saddle in place, since the ballscrew would just push it back! Then I could centerdrill the end. Threading wasn't bad, either

[blades]

Exellent! Glad to hear you were able to make some headway with it. Breaking through the case is always fun. I did my share of hard machining when I used to do it for a living, so I'm well aware of the many joys involved with it.