Hi all,

first a small introduction
I'm Adryan, studied for mechanical engineer (graduated 8 years ago) and work with my RF-25 mill and a lathe as a hobby. I also fly homebuild model turbine driven airplanes...enough for the introduction

After seeing the site of Jeff Davis, I decided to convert my mill to CNC.
The mill I have is a Rong-Fu 25 with a 1 bhp motor. It's one of the old models with a steel v-beld protection cover. I bought this machine second hand 3 years ago for $650.

I order the drawings and found out they didn't fit to my mill. The sizes of the RF-25 are quite a bit smaller.
I redraw most of the drawings using the drawings from Jeff as a guide and made some minor modifications (e.g. preload to the ballscrews)

Here are some pics of the rebuilding of the mill I'm starting this week.
-I cleaned-up the base and the x-y table
-I lapped the ways.....I know it's not everybody's favorite, but I'm very pleased with the result!
-Next was the priming and painting.
-Installing the x-y ballscrews

any chance of getting some more pics. also, i've got an RF-25 and was waiting to disassemble it to measure all the mounts for the ball screw nuts. if you can email me those drawings i would appreciate it. it will save me from disassembling, reassembling, machining, then reassembling and rebuilding.

jczub at hotmail dot com

Here are some more pics of the controller box I have made for it and of the parts for the conversion.
One thing I remarked when I removed the round colum, the were some thin shim plates beneath it. Has anyone seen this before on a RF mill?

yup, i had the shim plates beneath mine as well. i also had shims where the bearings go for the handles on all three positions.

The shims are put in to make the colum square to the table. When you re-assemble the machine, you will have to tram the spindle to the table. Make adjustments with shims in the same place.

Couple of questions...

What is that white stuff at the ends of the ball nuts? I realize you are using it for a wiper, but what is it?

You are using DB9 pin connectors for your steppers? If so, are your motors at a low enough current where they won't heat up?

Keep posing the photos and information! It's a great big help to those of us in the planning stages of such a conversion!

Thanks

Chris

Chris,

the white stuf is silicone. I first applied some oil to the screws then put the silicone on it. Let it dry overnight and than you can twist it gently and the "joint" to the screw will break.

The connectors I'm using for the servo's are speakon conenctors (see picture they are rated 20 Amps)
the sub-D 9 pin are for:
-encoder (one each)
-limit switches
-emergency switch
I also have 4 euro connector outputs for mill motor/pump/.../...

Today I worked some more on the mill and installed the limit switches for the y-axis (using microswitches ,IP65 sealed) and shielded cable.
This is also a litlle bit different to the plans from Jeff, but I didn't like having the cables/switched beside the y-slide.
I also made a lubrication connection to the bearings/ballscrews for central lubricating

Time for the next part,

I installed the limit switches for the x-slide (on the inside of the table so you don't see anything on the outside)
You can also see the lube line comming into the table for the bearing and the slides.
I also took apart the head of the mill, so I can grind it and repaint it. The top bearings in the v-belt pully are worn, so I have to replace them. I also think the bearings of the spindle are worn/dry because I can hear them ratling.
Does anyone know how to take the spindle apart? at which side should I start, and what an I expect?

i've taken my spindle appart plenty of times. you need to loosen the two nuts that are in your last pic on the previous thread. unscrew those and the spindle will pull out. on the bottom of the spindle the collar is screwed on not pressed on. the bearings are tight on the spindle and will probably need to be pressed off. i would tell you what bearings but mine might be different than yours.

spend another 6 hours today on the mill...
I cleaned all the paint and plaster from the head and painted it. You can also see the extra holes I've made for the cables from the encoder and servo.
Also in the front of the head is the enlarged hole for puting the Z-axis servo assembly in.
I took the spindle apart and found there were some fine chips in the lower bearing. After cleaning everything the bearings are still o.k.

some more work done this weekend....
I installed the z-axis servo inside the head, also the microswitch is inside.
I replaced the 3-wire cable for the power supply with a 5-wire so I can use one cable instead of 2. The power supply wire goes to the box on the motor.
..hope do do some sest runs next week.

Hello, your conversion looks great!

Can you please provide more details regarding you oil/lube configuration for the ways?

I am beginning to see more examples of this but no one has provided any details regarding its design and operation.

Thanks... Norman

Today I did some tests with the mill for checking the backlash.
on the X-axis I had 0.02mm (0.00078") and on the y-axis 0.06mm (0.0023").
With the z-axis I could very much notice there's no preload on the ballnuts. I had a random backlash from 0.05 till 0.1mm.
I tried fitting the spring (see picture) to create a preload on the nut, the backlash changed to a constant 0.05mm (0.0020")
Does anyone know if these values are normal, or can they be improved (tuning the servo's/increasing the preload)??


Norman,

I just grinded a z-shaped slit in the ways as can be seen in the pictures. The slot is about 2 mm wide and 0.5mm depth. I drilled several holes through the table base to get the possibility to connect it to a central lube-tube.

[QUOTE=adryan]Today I did some tests with the mill for checking the backlash.
on the X-axis I had 0.02mm (0.00078") and on the y-axis 0.06mm (0.0023").
With the z-axis I could very much notice there's no preload on the ballnuts. I had a random backlash from 0.05 till 0.1mm.
I tried fitting the spring (see picture) to create a preload on the nut, the backlash changed to a constant 0.05mm (0.0020")
Does anyone know if these values are normal, or can they be improved (tuning the servo's/increasing the preload)??
QUOTE]


It appears as though you have double ball nuts on each screw. You will need to adjust that to get rid of your backlash. Take the time now to do it right and don't rely on the backlash comp. feature in the CNC software to do it for you - you won't be happy with the results. Now, remember, to get rid of the back lash, you have to create some "binding" between the two nuts. There is a good article on a website somewhere and I will be darned if I can remember where it is. It also appears as though you are using rolled balled screws which may not have a constant pitch over their full length. This means you may have to adjust your ball nuts so that the backlash is compensated for in the "tightest area". Be prepared to spend a lot of time on this, the results will be well worth every minute of effort!

Chris

Chris,

on the z-axis is only one nut, because of the limited space, so I think I'll have to live with that.
Can the backlash on the X and Y (they are preloaded) really be brought back to zero? or will their always be some?

The Z axis is generally not as critical as the X and Y axis - but there are times when it is a problem.

You cannot get zero backlash - especially witha rolled screw. However, you do want it as minimal as possible and I don't know how close you can get it with a rolled screw. Even precision ground screws, with pre-loaded nuts etc., will have some backlash - .0002" or so. If there is truly zero back lash, then you are basically either in a "Bind" or very close to binding. If I were you, and I will be there later this winter I hope, I would do my darndest to get that backlash down to .0005" or less if possible.

CHris

I've reasembled the mill and found one small problem in the y-axis setup. I didn't screw the ballnut entirely to the aluminum bracket because I wanted to have the tubes of the ballnut on the top. To fix the ballnut in the bracket I used a small setscrew. Looking at it closely the ballnut could move a bit in the bracket when pushing hard. I now fitted some shims between the ballnut and the bracket so it can be screwed tight together. (see picture)

but now the real problem :confused:
I have the following setup:

encoder 250cpr
belt reduction servo 12 tooth - shaft 24 tooth
Thomson Precision Rolled Ballscew Stock- .631 x .2 Pitch
so if everything is correct:

250cpr => 1000ppr
i (reduction)=1:2
=> 2000ppr (pulse per shaft revolution)
pitch=0.2"=5.08mm
=> 2000 pulse/5.08mm =>393.70079 pulse/mm (entered as pulses/unit, and units are set up as mm)

In Mach2 I've set this up under motor tuning.
I've tried the setup again today and entered 0.1000 step and step mode in Mach2.
When moving forward/backwards the slide moves 0.15mm instead of 0.1mm (I've tried several times in same and in oposite direction)
When setting up 0.6000 the slide moves 0.90mm....

.....but when seting up 50.0000 step the slide moves exactly 50mm!!

I've tried another Gecko..another servo, but nothing makes a difference.

Am I doing something wrong????

It has been about a year since I setup MACH with my stepper motors. I remember getting myself pretty twisted around and messed up, so I wouldn't want to walk you through it with servos and encoders. You may want to post this on their yahoo group...

http://groups.yahoo.com/group/mach1mach2cnc/?yguid=175280003

Chris

Nice job, congratulations! I like how you went the extra mile and set up a lube system, and buried your switches out of the way.

You should be able to eliminate almost all of the backlash with those double nuts, at least all that your capable of seeing with that machine.

I dont think you will notice the Z axis on most jobs, I never have on any of my machines. As long as everything else is tight it will be fine.

Nice work!!

(The above oppinions are the authors and do not reflect those of CNCZone or its management.)

Finally got the backlash problem for the x and y slide solved. :)
Backlash is now 0.01mm (0.000393") for both, wich I think is very good....
I fitted a cover over the front part to prevent dust/particles coming onto the ballscrew.

I took the mill head apart again and measured the ballnut for the z-axis. There is about 0.1mm (0.039") play on it. The balls are 3.144mm so I'm going to try replace them with 1/8" balls (3.175mm) and see if I can get the backlash down a bit. Anyone tried this before on the Thomson ballnuts?

Just got the replacement balls of 1/8" (steel ones, 62Hrc)
What a difference! they fittet o.k. and when turning there is absolutely no slob! ...at least I can't feel any
So I'm going to try them on the z-axis.
Today I started working on a bench for the mill.
Basic parts are almost ready, just have to fit a pipe for letting the coolant out.

I'm thinking of using a pump of the central house heating for the coolant. Anyone tried this before?

:love:
very good job adryan

It took me about 6 months, but it's finally ready!
Here are the pictures of the finished machine!

I only have noticed a small problem with the first tests, perhaps anyone has a suggestion:
when the reset button of Mach3 is pushed the servo's quickly turn a little. Not much, but when it could be solved that would be nice.

Doesn't the keyboard make you a bit nervous.

Nice job.

Great looking conversion! Glad you got it done and I am sure someone with a servo system can help out with that last little "Tweak".

I love your idea with the keyboard being on extension slides - tucks out of the way nicely when not needed!

Good job! Keep us posted on some of the parts you make with it.

Chris

sweet

Adryan,
Great job, looks great.
Quick question, What grease did you use to lube
spindle housing to case, or upper casing to main
column. And what lubrication are you using in
your lube system?
Thanks

For the lube system I use Esso E-Febis K 68 Pail.
It's a thicker sort of oil used for the ways.
After speaking to the oil supplier they've told me they use is for the ways and the gears on some mills and laths wich have a central lubing system.
The grease between the spindle housing and the case is Esso Unirex EP2. I'ts a chain grease, very thick and sticking.

I still have to find out what's the best grease for using between the spindle and the v-belt pulley, because you can still hear a kind of a clattering sound from it.

rgds,
Adryan

Thanks, I just took my spindle apart tonight and I had the same
problem as you, grit in my bearings. I could not belive how much
came out of the bearings. Did you use the Esso Unirex EP2 for
the bearings?
I know that this is probably a stupid question, however what do
you use to force the thick oil down the oiling system, and how
often do you oil it?
Thinking about doing it to my machine, however it looks like a
lot of work.
Thanks
Chas

Adryan
How tight did you tighten the spindle bearing retainer?
Chas

Chas,

I use a lub system from bejur. It's a hand pump wich forces the oil through the tubing to:
-ballscrews nuts
-ways
-bearings used to support end of ballsscrew
the oils is a thicker "way oil" but it's comparable to the thickness of motoroil.

For the bearings of the spindle I used "wheel bearing grease".
This grease is also specialy made for tappered bearings, the same ones as fitted in the spindle.

When adjusting the bearings/nuts on the spindle carefully turn the inner nut a bit tighter. Next screw the outher nut against it (it will push the inner nut towards the bearing) check carefully if the play has gone. Repeat this untill you have it right.

Rgds,
Adryan

Thanks Adryan
I will be re-assembling my spindle this weekend and will
use your suggestions.
chas

just curious about the travel in the x and y with the ball screw conversion. did you lose travel when you put the ball screws and nuts in instead of the acme screws?

thanks

Jerry

what are your final x and y travel dimensions?

I had to step out and smoke a cigarette after seeing those pix of the finished machine.

Very professional!

Best,

BW

Jerry,

Here are the sizes you've asked for:

The travel is
x=231mm
y=155mm
z=93mm

This is what I've setup for on the travel limits in Mach3.

Here are also some pictures of parts I've made sofar.
First one is the aluminum demo from Jeff's site. Size a little reduced to 85x85mm.
Next one is a part I made for a small mini tractor. It's made of Fe355 (St 52.0)
The size is round 100mm. The 4 islands are 15mm in height.
Must say it's not good for the machine, because it vibrates to much when cutting the steel....just my opinion

rgds,
Adryan

If your familiar with the rf 30 and 31 do you think your yolk desighn on your rf 25 is the same. Dod you make this with a CNC and would you be interested in making one up for another cnc retro enthusiast?
Russ r1656@aol.com

Hello Adryan,
I´m retrofiting my rf30 i have a cuesntion what ballscrews do you used.

Hi,

I used the ballsrews from:

http://homeshopcnc.com/page3.html

You'll have great service from him. I would buy there again.

regards,
Adryan

info on z axis. adryan can you shed some light on how you tucked a motor up in there? i am having trouble installing my motor and drive assembly for the z axis. some more pics would be great if you have them.

thanks
Jerry

Sorry,

I don't have any more pics of the servo inside the "head".
I've attached a drawing of the assembly inside. The purple lines are the inside dimensions of the "head"

rgds,
Adryan

thanks for the pic. any chance of clearing that up a little bit, its kind of hard to read like it is.

thanks for the pic. any chance of clearing that up a little bit, its kind of hard to read like it is.

Zoom in or view in an image viewer. It looks very clear.

Any idea how much preload force you are running on the X and Y axis?

Adryan

Did you add the V channels on the carriage ways for oil distribution or did the machine come that way?

I increased the preload to 130lb for my RF30. Ball screws seem happy enough.



-Nick

Hi Nick,

I made the grooves myself, using a small Dremel tool,

regard,
Adryan

Hi all,

just want to let you know about the recent updates I've done to the machine.
I've fitted a 3 phase 0.75kw motor (1430RPM / 50 Hz) instead of the original 220VAC, including an ABB VFD 0.75kw.

To install the motor I had to make a small bush because of the diference in shaft sizes. This way I can use the original pulley and swap the motor any time.
Motor was easily fitted on the mill (same mountning holes used)
The VFD is on the wall next to the machine and controlled using the speedcontrol card in my controller (0-10VDC output)
The VFD is set up to go 100HZ max. The spindle can now go to 4100RPM instead of the 2150RPM. The bearing should be o.k..
I've also installed an spindle index sensor so Mach3 can correct the RPM if needed.
One thing I finally fitted (I think everyone thinks it's needed few install them) is the emergency switch. On the back of the switch I want to fit a connector so I can de-/attach a toolprobe easily.

Final picture is a a retracttable landing gear (F-16) I've made for my modelplane using the machine. Milling was done before the VFD had been installed.

regards,
Adryan

That is some beautiful landing gear you have made. I hope to one day have the tools and knowledge to build things like that. Also that is one good looking modifaction on the machine. I love the enclosed drive systems on the x-y axis.