Mini mill conversion Input apreciated

[cyclestart]

I would appreciate some feedback on what pulleys if you know any that would be more suitable than the chinese 3m pulleys

I've purchased pulleys from Chinese Ebay sellers and most suit my needs.
The ones purchased from Stock Drive Products (SPDI) have properly placed and sized bores and I can't say the same for some of the Ebay purchases.

[dazp1976]

These plum couples can transfer a lot of torque. They need "a bit of play" to compensate for axis misalignment. When they are to tight, they could get hot during use. I would not do anything about it until you are done and can measure the result (less backlash) of the changes made.

I will do X & Y using Nema23 2 Nm (283 oz) steppers. Z will be done using a Nema24 4Nm (566 oz) stepper (these are lying around). I probably keep the original spindles and will do backlash compensation in software. That way the primary conversion can be done cheap without a lot of modifications to the mill. For the controller i will use GRBL and TB6600 for the drivers (same as lathe).

True. Prob give as much/little lash as the spring type.
Only thing is (prob just me) I can't get a perfect circle in Mach3. Even with the backlash compensation on it comes out like a slight oval.
Any pointers on that one?
Everything else comes out pretty spot on.

[hfjbuis]

You have to compensate backlash at every change of direction. If you just move one axis, it is easy to compensate, just add the backlash compensation to the target. But in a circular move, there are 2 axis that change direction twice!
To mill a circle, you have to divide the circle in 4 quarters and then compensate for backlash before you cut each quarter.

This is how i do it on the lathe and it works fine!

[skrubol]

There might be some misunderstanding of backlash here. Backlash is lost motion with little to no force or torque applied. Springiness is not backlash. Gears have backlash but are typically very stiff. Timing belts and pulleys have little to no backlash with proper tensioning, but are not as stiff as gears. If you've got 1mm of loss in a timing belt, something is wrong.
As for compensation, in CNC mills usually the compensation is set per axis in the control, so the operator shouldn't need to explicitly do anything about it when using the machine.

[dazp1976]

[QUOTE=skrubol;2205372]There might be some misunderstanding of backlash here. Backlash is lost motion with little to no force or torque applied. Springiness is not backlash. Gears have backlash but are typically very stiff. Timing belts and pulleys have little to no backlash with proper tensioning, but are not as stiff as gears. If you've got 1mm of loss in a timing belt, something is wrong.
As for compensation, in CNC mills usually the compensation is set per axis in the control, so the operator shouldn't need to explicitly do anything about it when using the machine.[/QUOTE

With mine the backlash on the X is down to 0.03mm which I'm plenty happy with.
The Y is a different matter. It's all the same components but I have to have the Gib so tight it makes it a bit sticky.
Because the X2 table is quite small, if I have the Gib slightly loose the table tends to have a slight twist when under load.
Hopefully a bigger machine with a larger table will be a lot better.

[crl1_1]

Heres a little update on the Z axis. I was concerned the 1204 screws might not be enough but i think they will do the trick. I will be using a 2:1 ratio with a 425oz inch motor

[crl1_1]

Geting close to finishing the control box. I still need to add the limit switch and the 4th axis in the back and it still needs the on off button in the front.

[crl1_1]

Well i finally mounted the x axis. I still need to put the cover on but you get the idea

[kawazuki]

Jeez - you like over-kill engineering don't you! Everything seems to be twice as big as it needs to be. 425ozin steppers geared down 2:1 will make 850 ozin torque - massive for an X2 machine and paired with 4mm pitch screws will make it a bit slow. Too late now but a lot of these machines are happily running 270 - 280 ozin steppers direct 1:1 drive even on the Z axis. Fair play making / building your own conversion though!

[crl1_1]

Jeez - you like over-kill engineering don't you! Everything seems to be twice as big as it needs to be. 425ozin steppers geared down 2:1 will make 850 ozin torque - massive for an X2 machine and paired with 4mm pitch screws will make it a bit slow. Too late now but a lot of these machines are happily running 270 - 280 ozin steppers direct 1:1 drive even on the Z axis. Fair play making / building your own conversion though!

Bro where were you when i needed your input I wish I had received your advice in the begining but I the torque is around 600oz given the distance of about 3 inches. I would apreciate some light on this number if anyone knows how to properly calculate the number. I can always put another 30t sprocket to make it 1:1. I was also concerned with using larger ballscrews due to the size constraint

[rcheli]

Over the past year I converted an X3 using 381oz motors on the X&Y direct drive and a Nema 34 960oz motor on the Z geared but I forget ratio and the machine operates with no problem at all. I used the CNC Fusion kit with custom length screws for more X & Y travel and the deluxe ball nuts for zero backlash. I used Gecko G203V drives running 48 volts.

John

[dazp1976]

Jeez - you like over-kill engineering don't you! Everything seems to be twice as big as it needs to be. 425ozin steppers geared down 2:1 will make 850 ozin torque - massive for an X2 machine and paired with 4mm pitch screws will make it a bit slow. Too late now but a lot of these machines are happily running 270 - 280 ozin steppers direct 1:1 drive even on the Z axis. Fair play making / building your own conversion though!

I decided on direct drive with mine on the X2 with 425oz/in steppers on 1204 screws.

It's been running a while but has a few snagging areas that still need finishing. Had some changes done since the vid.



It's a bit of a bodge but I'd never worked with metal before and wanted to do the experiment to see if I could do it.
It works quite well for my needs and backlash is really minimal at 0.003mm.
My next build on an AMAT25LV (similar to the G0704) will hopefully be much nicer. Not in stock until t least mid October though

It's set up with dip switches at 1600 per rev and 400 steps per unit. Gives it 0.0025mm per step.
They are plenty strong enough, you can't go that fast with the 350w version X2 machine anyway. I've got rapids running 1200mm/min and the fastest I'm cutting is 700mm/min with a 6mm cutter at a DOC of 1mm. Any deeper or faster and it really struggles or overloads the spindle motor.

The 2 red lever valves to the rear right of the head are because I had to divert most of the coolant straight back into the container. There was so much pressure when it was first installed it was too much for the nozzles so needed calming down. Turns out that the diverting valve is fully open and the valve to the nozzles is open only just! A 350w pump was a bit much but blasts the chips away
I've made some new parts for it so I can change down to 8mm tubing rather than the 13mm yellow ones in the images. Want to thin it all out to make it tidier and maybe add another 2 lines.

[crl1_1]

I decided on direct drive with mine on the X2 with 425oz/in steppers on 1204 screws.

It's been running a while but has a few snagging areas that still need finishing. Had some changes done since the vid.



It's a bit of a bodge but I'd never worked with metal before and wanted to do the experiment to see if I could do it.
It works quite well for my needs and backlash is really minimal at 0.003mm.
My next build on an AMAT25LV (similar to the G0704) will hopefully be much nicer. Not in stock until t least mid October though

It's set up with dip switches at 1600 per rev and 400 steps per unit. Gives it 0.0025mm per step.
They are plenty strong enough, you can't go that fast with the 350w version X2 machine anyway. I've got rapids running 1200mm/min and the fastest I'm cutting is 700mm/min with a 6mm cutter at a DOC of 1mm. Any deeper or faster and it really struggles or overloads the spindle motor.

The 2 red lever valves to the rear right of the head are because I had to divert most of the coolant straight back into the container. There was so much pressure when it was first installed it was too much for the nozzles so needed calming down. Turns out that the diverting valve is fully open and the valve to the nozzles is open only just! A 350w pump was a bit much but blasts the chips away
I've made some new parts for it so I can change down to 8mm tubing rather than the 13mm yellow ones in the images. Want to thin it all out to make it tidier and maybe add another 2 lines.

Wow that is quite impressive I noticed yopu are using 425oz on the z, is that correct? I may have gone overboard with my belt drive but I wanted to make sure I had enough power I am currently looking to upgrade my spindle but I am having a tough time finding and adequate one

[dazp1976]

Wow that is quite impressive I noticed yopu are using 425oz on the z, is that correct? I may have gone overboard with my belt drive but I wanted to make sure I had enough power I am currently looking to upgrade my spindle but I am having a tough time finding and adequate one

Yes. I'm using a 425oz/in on the Z but...
To be honest, to me it's lacking down force when it comes to drilling. It can't go down very quick at all otherwise the stepper motor stalls with a bumping noise as it misses steps. You do have the right idea going a bit bigger imo. Perfect for milling but drilling... no.
Like when you drill by hand you need to put a bit of pressure on it otherwise you just rub the material and burn out the drill bit.

In terms of drilling, for a while now I've been using the conversion only as a spotter then my other manual X2 for drilling the spotted holes.
For instance what used to take about 2 mins with a 4mm drill bit on the conversion takes 30 seconds on the manual one without the heat or wear.

[crl1_1]

Yes. I'm using a 425oz/in on the Z but...
To be honest, to me it's lacking down force when it comes to drilling. It can't go down very quick at all otherwise the stepper motor stalls with a bumping noise as it misses steps. You do have the right idea going a bit bigger imo. Perfect for milling but drilling... no.
Like when you drill by hand you need to put a bit of pressure on it otherwise you just rub the material and burn out the drill bit.

In terms of drilling, for a while now I've been using the conversion only as a spotter then my other manual X2 for drilling the spotted holes.
For instance what used to take about 2 mins with a 4mm drill bit on the conversion takes 30 seconds on the manual one without the heat or wear.

I suppose it was good then that i did the belt driven then. I am geting close to mbeing done with the machine

[crl1_1]

Well i decided to upgrade the spindle

[dazp1976]

Jeez - you like over-kill engineering don't you! Everything seems to be twice as big as it needs to be. 425ozin steppers geared down 2:1 will make 850 ozin torque - massive for an X2 machine and paired with 4mm pitch screws will make it a bit slow. Too late now but a lot of these machines are happily running 270 - 280 ozin steppers direct 1:1 drive even on the Z axis. Fair play making / building your own conversion though!

Surely should be able to get 1000mm/min at least for rapids which isn't too bad for a mini mill.
Setting the driver at 3200 and the steps per at 800 would equate to 0.005mm per step for a 4mm.
If I have the math right, on a 200 step motor and 4mm screw that would be 0.01mm per step with a 2:1 drive.
I think that would be near enough myself.

Mine is direct drive with 425oz/in and mach shows a max velocity of 3000+mm/min. However I can only hit 1300 without stalling with rock tight gibs and I have my thrust bearings way too tight as well which needs rectifying, then it should be a bit better, atm I think it's poor. Mine works out to be set at 0.005mm per step.

With the 2:1 drives on ctrl1-1's it should be able to get further up the velocity scale than mine can with that much torque surely?

[crl1_1]

Surely should be able to get 1000mm/min at least for rapids which isn't too bad for a mini mill.
Setting the driver at 3200 and the steps per at 800 would equate to 0.005mm per step for a 4mm.
If I have the math right, on a 200 step motor and 4mm screw that would be 0.01mm per step with a 2:1 drive.
I think that would be near enough myself.

Mine is direct drive with 425oz/in and mach shows a max velocity of 3000+mm/min. However I can only hit 1300 without stalling with rock tight gibs and I have my thrust bearings way too tight as well which needs rectifying, then it should be a bit better, atm I think it's poor. Mine works out to be set at 0.005mm per step.

With the 2:1 drives on ctrl1-1's it should be able to get further up the velocity scale than mine can with that much torque surely?

I fired it up today i tested only 900mm/min it actually sounded really nice, and the Head moved without any issue. I was concerned it would be too much weight but the new motor is lighter than the old one. I am also moving the electrical box to the colum to make it as light as possible. You can can get a better idea in the video
Here is a video

[dazp1976]

[QUOTE=crl1_1;2217356]I fired it up today i tested only 900mm/min it actually sounded really nice, and the Head moved without any issue. I was concerned it would be too much weight but the new motor is lighter than the old one. I am also moving the electrical box to the colum to make it as light as possible. You can can get a better idea in the video

General consensus is that some kind of counterweight helps on the head.
The steppers take them down easy, any problems usually arise when they are lifting it back up.
Shouldn't be a problem though with the torque you have unless you get the head drop issue while cutting. Then you may need to look into gas struts for it.
Head drop is why mine has the brick/pulley bodge. Isn't worth me doing the struts now if I'm replacing the machine.

[crl1_1]

[QUOTE=dazp1976;2217380]

I fired it up today i tested only 900mm/min it actually sounded really nice, and the Head moved without any issue. I was concerned it would be too much weight but the new motor is lighter than the old one. I am also moving the electrical box to the colum to make it as light as possible. You can can get a better idea in the video

General consensus is that some kind of counterweight helps on the head.
The steppers take them down easy, any problems usually arise when they are lifting it back up.
Shouldn't be a problem though with the torque you have unless you get the head drop issue while cutting. Then you may need to look into gas struts for it.
Head drop is why mine has the brick/pulley bodge. Isn't worth me doing the struts now if I'm replacing the machine.

I was thinking about using the spring loaded arm that comes with the mill to help with the lift. I just ordered a 35 lb gas strut I will mount it on the side to prevent the head drop. Thanks for bringing this up I was not aware of such thing