I have a HF benchtop mill/drill I got several years ago that I have been wanting to convert to CNC for a while. I'm not sure the HF model number, but the specs are the same as the Grizzly G3358 http://www.grizzly.com/products/item.aspx?itemnumber=G3358

I only plan on a 2-axis conversion at this point and have some stuff that I am wondering if they are sufficient for the conversion. First, I have 2 Superior Slo-Syn steppers one has a 300 oz-in hold and the other has a 450 oz-in hold. I also have a Stepperworld FET-4 controller board.

I plan to convert this one at as low a cost as possible. I will be installing rolled ballscrews on the X and Y though. My plan is to ultimately use this one to make parts for a larger square column mill drill. This one will then be retired and sold, or given to my father. I would really like to be able to use what I have right now.

So here are my questions.

Are these steppers appropriately sized for a 1:1 drive?
Would I be better off with a 2:1 drive?

I'd like to stick to a 1:1 drive for simplicity, but if it ain't gonna work then I can do the 2:1 or even more.

Also Can the FET-4 drive these steppers, or do I need to look for other controllers?

Thanks in advance,

John B

I am guessing (it is a guess) that you would be OK with 2 450 oz steppers. I think the 300 would be too weak.
Gearing steppers down can actually give you less torque. The faster the stepper has to spin, the less torque it creates. Torque curves for your stepper will shed some light here.
I have no experience with the fet4, so can not comment there. If you are planning on staying with steppers, I would recommend getting Gecko's.
Colin

i just started my mill-drill conversion today, and i am using some nema 23 vextas, i originally thought that there was now way that they would do the job. i think they are like 150 oz motors. any who, the x axis was no problem, of course it has thrust bearings on it. the y axis was what concerned me. there is no bearings from the factory on it. mine is a speedway series, but i doubt there is much of a difference between that and the others. so what i did was removed the bearing carrier, y axis screw mount or what ever you want to call it, and i clearanced it out so i could add a thrust bearing. i am always on a tight budget so i usually look around my junk piles to find pieces and parts. the bearing came from a c-band satelite actuator gearbox. i then add another to the other side of the y mount. it was a huge difference from stock. the y axis feels as silky smoothe as the x. although i would love to convert it to ball screws, i am afraid it will not be in the budget for a while. but the way the machine feels now, i am not to worried about it.

i am hoping that tomorrow i will be able to finish the conversion, minus the limit switches, coolant and other accessories.

Hi 109jb

i have a similar machine converted it to cnc about 3 years ago im running 200 in-oz stepper and 1:1ratio they work fine haven't lost any steps yet on a job the z has a 2:1 ratio off the stepper and will drill at an inch a minute with a 3/4" drill in mild steel thats better than i can do by hand
i have actually just started to convert to ball screws the 3 thou backlash just suckes hope this helps

cheers
peter

Hi 109jb

i have a similar machine converted it to cnc about 3 years ago im running 200 in-oz stepper and 1:1ratio they work fine haven't lost any steps yet on a job the z has a 2:1 ratio off the stepper and will drill at an inch a minute with a 3/4" drill in mild steel thats better than i can do by hand
i have actually just started to convert to ball screws the 3 thou backlash just suckes hope this helps

cheers
peter


What kind of feedrates under light/medium chiploads are you getting with this setup?

If 200oz/in steppers are working on that mill at 1:1 without loosing steps with leadscrews, I'm thinking the 300-400oz/in DC servo's with ballscrews I'm planning should absolutely fly on a machine similar in size to the original posters.

Thanks! :)

hi PeteZ28

i was cutting aluminium last night with a 5/8" end mill full cutter width at a depth of .1" and 30 inches a minute spindle speed 2500rpm
it actually started to stall the spindle but not the motors

stepper are 1:1 onto a 10tpi lead screw just plane old square thread
i have smashed a few 1/4" endmills off trying to feed to hard

im looking forward to getting the ballscrews on to get rid of the backlash should be sweeeeet

i think you will have a good machine with that setup

cheers
harty

Harty, thank you so much for the reply. I've been trying to get an idea of what size servo's I should use and asking questions on a bunch of forums. All I keep getting is the "depends on the application etc etc" and all I keep asking is what have OTHER people used and what was their results. Seemed like a pretty simple question and I thank you for finally answering it :)

Pete

Edit: Oh, what machine are you using that on? I'd love to see a few pics of your setup, thanks!

hi pete

my machine is in bits at the moment for the ballscrew conversion i will post some pic's of the conversion and the mill when its finnished
that should be in a couple of days

cheers
harty

here are the pics fo my ballscrew converson hope this helps

some more

this is the last of them and it sure is nice to get rid of that backlash

cheers
harty

Harty,

That's a pretty nice looking ball screw conversion. I still haven't done my conversion yet because I just moved and am still getting settled. It sounds like my steppers will work, but I have a few other questions.

Here are the ballscrew questions
1. What size ballscrew are you using?
2. Are you using just the stock bearings for the leadscrews, or did you add anything (ie: needle, thrust, etc..)?
3. Are both ballnuts threaded into the aluminum blocks, or is one threaded and the other spring loaded to take backlash?
4. I see in one picture, the ballscrew comes through the belt sprocket, but others look like you are using an adapter with set-screws. Can you elaborate on how you are taking care of thrust and power transmission?

Other Questions
1. What stepper controller are you using?

Thanks

John B.
AKA 109JB

Harty,

I forgot to ask, How well does the Z-axis work with driving it throught the factory "fine feed". My z-axis has a good amount of slop. I was thinking about that method, but am leary because fo the slop.

Thanks again,

John B.

Hi john

the ballscrews are 5/8 and there 5tpi
i am using stock bearings just added a brass bush to the end od the x axis where the belt sprocket is
both the ballnuts are threaded into the mounting block and you just screw one in or out to remove the backlash and then lock with the grub screw
to set this up all i did was put 2 nuts on the thread wind them in till the gap in the middle was bit bigger than the mounting block then measure the distance from the outside of one nut to the other then remove the thread then screw both nuts into the mounting block till the distance was the same as measured and inset the ball thread works a treat

y axis drives from where the original handle was which uses the adapters shown
the x axis uses the adapter to handel the backlash the i just drive straigt to the tread with the pulley held on with grubscrews at the other end i did this cos the machine was setup that way when i did the cnc conversion 3 yeas ago
im using propriery stepper controllers and motors not sure of the brand but they come out of some suplus photographic machines they are also 5 phase which meas you get 500steps per revolution so at 5tpi 1:1 to the motors you 2500 step per inch
the zaxis has heaps of backlash i have ballscrews to put on this but its a bit more work also its not much of an issue for me as i dont do much profile cutting