The ParaCNC experiment

[Parameter]

Hi everyone, I really enjoy reading you guys and learned a lot here. This is my first thread and it's about the machine I'm building so I'll keep it simple as it should get long.

I'm building a 3 axis mill, and may add the fourth axis in the future on the table. This is a fixed gantry model derived from the JGRO plan. Here is a bit of specs:

REQUIREMENTS

mill foam to cast the parts in aluminum using the Lost-Foam method
mill and engrave plastic for small projects and cases faces
mill and engrave soft-wood for carving small windmill propellers (4')
mill and engrave MDF for patterns to cast in sand and build the next-gen mill
engrave PCB boards so I can dispose of that dangerous ething fluid.

FRAME

Type: Fixed gantry
Material: MDF and particle board for the base board.
Work area: 24 x 18 x 4.5 inches
Shafts: X and Y = 3/4" or 1" gas pipe, Z = 5/8 cold rolled steel.
Bearings: ABEC-4 and ABEC-5 roller-skate bearings
Leadscrews: For now I consider 5/16 or 3/8 all-thread, the motors are small
Leadnuts: Home made in cutting board plastic. Has backlash adjustment using a slot and tension screw.
Motor Coupling: Direct drive using air-hose and screws
Precision required: 0.005"
Limit switch: Old calculator buttons switches OR hall switch setup, maybe as an upgrade

ELECTRONICS AND CONTROLS

Controler: (tested today, it works, gotta find a metal case and mount it)
3 axis home made using the CW-Tech board. It's using the UCN5804 from Allegro and has a STA401A chip added to it to control 4 120v relays and the back-emf protection diodes are on the board so they cannot be bypassed or forgotten when installing the relay board.

Relay board: (board pattern is done, need to etch and solder)
Home made relay board, the 4 relays can take 15 amps each and all are diode protected. Those will control standard house plugs on 115V 60hz. One is for the spindle (1A dremel), the other for the vacuum cleaner (4-6A), the third for a 25W hallogen projector and I don't know what to do with the fourth...

Drive boards:
3 x 1 axis driver boards made with (1) STA401A NPN darlington arrays taken from an old printer. Those can take up to 4 amps but require me to put a gate inverter at the input to take the 5v output to ground from the CW-tech board as this would not be necessary with PNP arrays... well... it's free and the inverter too as it comes from the same printer board.

This board design will then be modified for anything powerfull I can find, maybe even bridge some STA401 together to handle 8A per stepper or more when I find better motors.

Power Supply:
I got 2 really nice 28V 2.85 Amp from old apple printers. So I may be able to use those in parallel for a total of 5.7 A of FREE transfos at 28V...

But a computer power supply is rated at 20A 5v and 10A 12v... I know its not really good power tough but I used to take this for my 2 axis foam lathe and charge the 5v side to get more power on the 12v side... it works...

Chopper/PWM:
This is an area I really am not too familiar with but I understand how it works. Using the above power supply, it would be too much for my 3V steppers and resistors would REALLY heat the shop at 28v... So I was thinking about building a PWM board using a chip with built-in sensor and use some of those STA401A as power transistors for the PWM switching using the 4 channels in parallel.

Now, do I need 1 load sensor for each motor, each coil set or 1 for all together?

Computer:
I have a Pentium 233 MMX with 8 gigs of hard drive and 128megs RAM... plenty power.

Software:
TurboCNC on FreeDos. If I ever make it commercial, I'll make sure that the Dak guy gets it's registration money... For now I'm just beginning and the cash goes on the machine... Still, I thank that dude for such nice software.

STEPPERS

Got 2 from old apple printers which I found for 3 bucks each at goodwill store. They are 6 wires with 1/4" shaft. I can't find specs on those, but I guess they are quite common... Here is the label writing... TEC Stepping motor, CBA45-01101, VOLT 3v, DEG/STEP 1.8, COIL 3.5 ohms, Tokyo Electric Co. Ltd. if someone knows about those, I'd love to know what size they are and their torque rating. I figure they must be nema 17 or something (about 2 round x 2 deep).

The other one is a little bit smaller, runs at 3.1v and is tagged PJJQ114ZA-K which is also 1.8 degrees per phases. Internal coil resistance is 3.4 for this one. Made by Kyushu matsu****a electric. Its about 1 5/8 x 1 5/8 x 1 1/4 inches.

These are the best I found up to now. I have a savin photopier that is maybe waiting for dismantling, If I could find some better motors in there, it will go. Maybe I'll buy that 20 bucks photocopier I seen the other day if this is a good source of good unipolars.

SPINDLE
For now I will use a cheapo dremel tool of the Yoca brand (whatever...). I ache at the 1/8" capacity and will consider buying a router and flex-shaft in the future to do the wood carving. I could do only foam as a start then upgrade the motors and spindle.

Well, jee, that was long, but I hope everything is there. I'll try to post some pics as soon as I get access to a working camera. (Momy, can you lend me your camera please??? lol )

Any comments?

Para

[mxtras]

You will have better results if you shorten things up a bit - one question at a time.

Our attention span does not equal your enthusiasm.....other than that - no comment!

Scott

[H500]

You need at least 2 sensing resistors per motor. Two coils are normally driven at the same time if you want max torque.

[Parameter]

I do understand about the shorter post issues but I would like to make it a bit like a diary... You may step in with comments anytime.

Well, this should be done within 3 weeks, let's see...

Para

[ignatz]

Hi Para,

It sounds like you have a good plan. I have a couple of pointers from my experience building a machine by hand. Take them for what they are worth.

#1. Leadscrews. I used 1/2-10 ACME screws. I think this was a mistake. I should have used a screw with a common tap size. I made a homemade tap but it added a week to the overall build time.

#2. Couplings. Initally, I made some DIY aluminum couplers. These worked but had problems. I ended up buying 3 Lovejoy couplers for $20 shipped. The Lovejoy couplers work much better than my DIYers. I have no experience with air hose couplers but most of the suggestions I've seen indicate that you should use fuel hose with re-inforced braiding and I couldn't find a local source for the hose. The LoveJoy couplers make up for misalignment and have some vibration reduction capabilities.

A good possible source for steppers are HP LaserJet printers. These things are pretty common in thrift stores (in my area) and computer shows.

Have you seen yukonho's machine. It might be a little bit closer to your design than JGRO's plans.

Would you mind sharing your relay board plans? It sounds like a nice feature.

How far along are you on the casting portion of your experiement? I am 80% complete on the construction of my furance. I put that project down to complete my CNC router because I realized I'd have nothing to cast without it.

I hope this helps.

[Parameter]

I've been casting for more than a year now but my furnace is quite small. I just made a waste oil burner, need more experiments.

As for the CNC, most parts are done, the base, x, y and z axis are done but still need to mount the X table and the Y carriage assembly as well as the steppers. Lead nuts also have to be done... Sorry no pics but I'll show it off when ready for sure...

I had to do a couple compromises and changes but all seems well... we'll see...

Para

[Parameter]

Well.... My MDF CNC machine is done, the motors are installed, the controler is ready but...

1- I need the motor resistors... 60watts each... might as well buy some heating element and wind it myself... lol You guys would know a good source for resistors of this wattage, cheap and in canada?

2- The home switches do'nt seem to work in TurboCNC but it does work just looking at the parallel port inputs using F2 in active mode... Any idea how to configure this all right? I did went in port configure and set it right... still...

I'm using the CW-Tech 3 axis board and all seems fine... I'd rather have a modular design tough... next time... Also have to wire the limit switch but that can wait...

3- I have'nt figured out the new motor wiring and I stupidly lend my dm and the guy is gone for the day... I can't help to repeat to myself... don't, next time just don't...
(I have a pre-wired 12 v stepper I did a lil while back to test my controlers which use the same db9 connector and pinout so I could test all the axis)

4- The roller blade berings did well for the Y and Z axis but the X axis seems the flex way too much (30 inches on 1/2 gas pipe...). I need to add some support bolts. Adjustment of the table bearings is not easy... to say the least.

Well... I can't wait to try the thing... I learned so much and will, of course, build another one as I enhance this one... Sorry to all, I really have to buy a new camera... I can't believe I did'nt take any picture yet...

Para

[buscht]

Para, I just found your post.
A couple of things, mostly minor.
I doubt if you will be able to hold .005" precision with this machine. +-.016" would be fantastic.
1/8" collet is OK for this size machine, steppers and drives. I mean that everything is proportioned well, components, power, etc. If you want to move up to a larger router, you should consider that for the next project.
Can't comment on the electronics as that is way over my head.
Trent

[Parameter]

True, I won't get 0.005... I see the flex in my spindle mount and will have to cast one in aluminum as soon as I can mill the part. Many parts will be cast an replaced by the aluminum casting. With foam parts, If I get around 0.01 it should be fine... I'll include some screw adjustments this time!

This includes the Z carriage and dremel mount AND the X linear bearings... Some flex should go out as soon as I go to 1 inch pipe on the table...

Thanks for the evaluation Buscht, I got my wiring right yesterday very late (well, this very early morning?) so I'll be able to mill my first part today... geeee, feel like soon to be dad....

Para

[Parameter]

Weeeeeeeeeeeeell.... It works! That's just so cool...
So I have around 20 x 14 x 4 but its all woobly... lol

I get around 16 ipm with 5/16" all-thread on X and Y
Z is around 6 ipm since it's grossly underpowered. (motor is less than 1.75 x 1.75 size)

I now know that my X table is not straight as the table attachment make it a bit hard to adjust... My engraving is nice then too deep as the spindle engrave in to the other end of the table. We need something better for the home made linear bearings...

I also get a lot of flex because of the way too heavy Y/Z/Spindle assembly or maybe it's the rods that are too thin? lol The support screws are a must but I'll upgrade the shafts to 3/4" (y) and 1" (x) or something like that.

Well, I'll be in the garage everyday now... thanks to all for the inspiration...

He, building a CNC machine in 3 week is possible! Well, depends on what you wish for...

Para

[Parameter]

Oh yeah, also, I tested without resistor on the motors but it was 3v motors on 5v supply. I know I could'nt play with it too long but I had to see the darn thing move...

And move it did. It took quite a while before they got hot to the touch, but then my X motor, wich was the one working hardest on this part, lost a few steps. Is this possible that this is related to heat? I stopped right away of course...

I did upped the rev on this one, maybe a couple hundred hz too much... it was fine until it dived in the last letter. Good motors are a must, now I know...

I understand what you guys meant when you say a dremel is a clunky spindle... Now Imagine one of the cheapo imitations... well... it sucks... So now a rotozip is now on the list... Any suggestion for the same size biggest bang for the bucks? A small porter router?

Also... Would you guys have a souce of good bits for 1/8" dremel? I tried using sharpened nails but I can't wait to tackle some pine wood with a good 1/8" ball mill... seem soooooo fun... I will make sand molding patterns so I can cast them later...

I'm just so happy, sorry guys If I explode but hey!

That's my baby and she Walks! Woooooooohooooooooooooo

Para

[H500]

Congrats Para! I remember how I felt when I got my first machine going.

You should run your motors with a chopper drive and about 30 volts. You'll be surprised by how much better the speed is.

Princess Auto sells surplus carbide bits for about $9 for 10. If you're just cutting wood, they'll probably stay sharp till you snap them.