Bipolar / Unipolar n trimers

[transtar]

Can anyone advise me on what the difference between Unipolar and Bipolar stepper motors. Also, what the best brand of trimer / router should I used? I am using my machine for about 6 hrs a day.

Thanks and happy routing

[geoff p]

Hi Transtar,
Essentially there is little practical difference between them in small sizes though you will find very few Unipolar types at more powerful ratings. And believe-you-me, as the cnc-bug grips you, you will want more power then you began with, because you will almost certainly push the limits of your machine's capabilities for speed, cutting-rate etc etc.

I would suggest starting with Bi-polar motors because you will more likely get away with fewer system-changes when you upgrade to larger motors but bear in mind that the controller will be a tad more expensive - excuses of more transistors etc etc. You should keep in mind that higher-current motors generally perform better at decent-to-higher speeds. I recently made the mistake of buying some 200 oz-inch motors with the remarkably low current of 0.6 A (600 mA) and they do not perform a half as well as my 100 oz-inch jobby at 2 A; their speed is restricted, severely, so I have to run them with step-up gearing to propel my axes at better than a crawl.

Beware also that advertised torque may be Detent-torque or Holding-torque. The latter is what you need to scurry your router-head around the job; refering back to my 200 oz-inch - it turns out that is their Detent-torque and is about three-times their Holding value. But the advertiser didn't make it clear so I bought a 'pup'.

If I seem to be pushing the speed aspect too much, remember you are moving a router, whose cutter spins at 25-30,000 RPM, so it needs to travel quickly to keep cutting rather than rubbing the work.

As for trimmer/routers, I can only suggest getting one with 1/2 inch collets: my own ancient Bosch requires 1/4 inch shanks cutters and these are very difficult to find in Thailand.

You don't make it clear if you aim to buy a CNC-machine or are you setting out to build one?
Chok Dee (good luck)
Geoff

[cncpilot]

I was just reading these articles on the web last night. Check out this link. unipolar vs bipolar tutorials at stepperworld .com

[transtar]

Originally Posted by geoff p Hi Transtar, Essentially there is little practical difference between them in small sizes though you will find very few Unipolar types at more powerful ratings. And believe-you-me, as the cnc-bug grips you, you will want more power then you began with, because you will almost certainly push the limits of your machine's capabilities for speed, cutting-rate etc etc. I would suggest starting with Bi-polar motors because you will more likely get away with fewer system-changes when you upgrade to larger motors but bear in mind that the controller will be a tad more expensive - excuses of more transistors etc etc. You should keep in mind that higher-current motors generally perform better at decent-to-higher speeds. I recently made the mistake of buying some 200 oz-inch motors with the remarkably low current of 0.6 A (600 mA) and they do not perform a half as well as my 100 oz-inch jobby at 2 A; their speed is restricted, severely, so I have to run them with step-up gearing to propel my axes at better than a crawl. Beware also that advertised torque may be Detent-torque or Holding-torque. The latter is what you need to scurry your router-head around the job; refering back to my 200 oz-inch - it turns out that is their Detent-torque and is about three-times their Holding value. But the advertiser didn't make it clear so I bought a 'pup'. If I seem to be pushing the speed aspect too much, remember you are moving a router, whose cutter spins at 25-30,000 RPM, so it needs to travel quickly to keep cutting rather than rubbing the work. As for trimmer/routers, I can only suggest getting one with 1/2 inch collets: my own ancient Bosch requires 1/4 inch shanks cutters and these are very difficult to find in Thailand. You don't make it clear if you aim to buy a CNC-machine or are you setting out to build one? Chok Dee (good luck) Geoff

Thanks for the advise, basically I am building a fixed bed with moving gantry type of cnc machine for my home used. I have no problem with the mechanical design aspect of the machine cos I owned a fully equiped precision machine shop, unforunately I can't say the same for the drive and control side of the system. I am completely open to all suggestion. Matter of facts I was thinking of using Bipolar stepper motors of 200oz torque for X and Y axis and a smaller motor for the Z-axis. But after reading your post mentioning that you made the mistake of buying some 200 oz-inch motors with the remarkably low current of 0.6 A (600 mA) and they do not perform a half as well as my 100 oz-inch jobby at 2 A, I am now quite lost. In your personal opinion do you think I should use a 100oz motor instead of 200oz motor? I was actually looking at the stepper motors being sold by RS components together with the drivers etc which is widely available. If you have a similar RS catolog you should be able to see that they do have a wide range of stepper motors. As for trimer, I am looking at Makita brand.

Btw, do you owned a cnc machine? if so what size , motors and drive set up? I am asking cos I may want to used your setup if it is suitable to me.

My machine specification:

Travel: 1,000mm x 350mm x 100mm
Type: Fixed bed with moving gantry guided by linear ball bearing on Hardened
chromed shaft

Thanks

[transtar]

Originally Posted by cncpilot I was just reading these articles on the web last night. Check out this link. unipolar vs bipolar tutorials at stepperworld .com

Thanks, I will certainly read it.

[geoff p]

Hi Transtar,
Yes I have a home-made cnc router; some of the electronics I scratch built and some I bought in kit form. The actual travels achieved are 500 x 400 x 50 mm. Control is by Mach2 in Demo mode - I will buy it when I have finished ironing-out the snags in my 'mechanicals'. So far my outlay has been about 20,000 baht or 300 pounds or 500 dollars US, including hardware, electronics, and motors, but not the router. Most of that went on electronics and motors.

My frame, to give it a more glorious term than it deserves, comprises two ends of 15mm plywood (about 4" x 30") separated by conduit as X-axis rails about 850mm long.

These end pieces are woodscrewed to the base (1 inch ply - 'cos it was there!) via small steel brackets. It all rests on top of a once-upon-a-time twin tub washing machine casing, which now houses my electronics and power supply.

The gantry, as some of you call it, is one round tube and one square tube spacing two substantial blocks of wood. These 'bogies' run along the X-axis on skateboard bearings, presently relying on dead-weight to keep them down.

My X- and Y-axis screws are supported in bearings outside of one rail. They are 5/8 UNC threaded rod and the nuts (sorry, followers) have a bit of iron welded-on for atachment to the carriage. I had a local machine shop turn the ends of the rod to 8mm dia to suit skateboard bearings and threaded M8 about an inch for a clamping nut. Said nut clamps the inner bearing-race, a spacer and a timing-belt pulley.
A bloody-awful mess comprises the Y-carriage carrying the Z-axis. Some more about that another time.

Motors! My Z-axis carries the full weight of both itself and the 1.5 Kg of the Bosch POF500 router. As the travelling part is a lump of 3mm plate plus guides, we are probably talking about near up to 3 Kg. A 100 oz-inch motor from IM Automation in Bangkok drives this soooo easily. The motor is rated for 2.5 A but I drive it at less for the sake of my driver electronics.

On the other hand, for X- and Y-axes I bought 200 oz-inch motors from Ocean Controls in Australia. They are hopeless! At stationary but with power applied, I cannot budge them by hand - good. But when stepping, and at their rated 600mA a light touch of finger-and-thumb simply stops them - Not Good!
Their coil current is low because their resistance and inductance are high (12 ohm and 43mH respectively) == not suited to high speed, so I cannot gear-down to gain torque at decent speed. Take a look at http://www.active-robots.com/product...r-motors.shtml where you will find (about halfway down the page) Sanyo Denki 103H7123-0151 rated at 7.35 lb-inch (~117 oz-inch) and Ohm/Phase: 6.7, Inductance/Phase: 15.0 mH, Current/Phase: 1 Amp or their next item Sanyo Denki 103H7123-0440 (also 117 oz-inch) but Ohm/Phase: 1.6, Inductance/Phase: 3.8 mH, Current/Phase: 2 Amp. Of these, the former will be better suited to low speed while the second one will maintain torque at higher speed due to its lower inductance. (I am not suggesting these 117 oz-inch motors for your purposes.)

When I save enough I will certainly replace these two with high-current, high torque motors of a reputable make (like IM, mentioned above)

Sorry to go on so much. I didn't mean to get you lost. IMHO use a 100 oz-inch motor for the Z-axis and 200 oz-inch for the X- and Y-axes. You are probably not looking for speeds in the hundreds-of-inches-per-minute range (like some commercial machines) but as I said before, the cutter needs to cut not rub the work.

For drivers, I use KT5191 (L297/L298 combos) bought from Ocean Controls and they are excellent. Having hammered the motors, I reckon I should also publically praise Peter Simmonds of Ocean Controls for his patience with me and great service. Thanks Peter.

Yonks ago I started to make some sketches of my machine but I got carried away with 'just fix this/improve that...' I will do more, and soon.

Geoff

[transtar]

Hi geoff p:

Thanks for the description of your machine. My design that I am currently working on is much more robust than your design. To start off I used alot of scrap / left over materials in my shop especially aluminium sheet and bright drawn mild steel (BDMS) rectangular bar. My machine bed is actually a piece of precision pre-milled alu sheet of 12 mm thick, it is supported under with 3 pcs of 12mm x 38mm BDMS bars. Both end of the bed has a 25mm thick x 100 width BDMS screwed. These two end pieces carries a dia 25mm hardchromed plated hardened shafts. On these two shafts a gantry build up from various thickness of alu sheet is being build up. All these slides on two pieces extra long linear ball bearings. The Y and Z-axis also slide on similar but smaller dia hardened hardchromed shafts. All thick BDMS components has being lightened by milling hollow or holes. The total cost of the machine? I dun have any idea yet cos I have yet total all my cost. I intend to drive my Z-axis using timing pulleys with the motor, the reason is that I found out that I may need counter balance if I mount the motor direct onto the drive shafts.
My drive shaft for X-axis is M20 x 4mm pitch and the other two axis is M14 x 3mm pitch.

Since you mentioned that your motors setup is more or less acceptable to you, I want to use your setup as initial stage for experiments. Can I know what brand of motors you are using? I am thinking of using Oriental or Sany Denki motors. These two manufacturers has sales offices in Singapore. Any suggestion?

Btw, what are you using the machine for, also are you staying in Bangkok? I always travelled to Bangkok for buisness. I was thinking maybe I can visit you on my next trip there.

Cheers and happy cutting!

[geoff p]

Hi Transtar,
You're right, your machine is a lot more substantial than mine!
I actually use timing-belt drives for each of X- and Y-axes but a gear drive on the Z, primarily because I had them in the junk box. The former are ~about~ one to one but the Z is geared down 2:1 then drives a 5/16UNC threaded rod. In Phuket it is near impossible to obtain all metric 'stuff' so I use what is available and let the software do the conversions as required.

I'll put up some sketches of my setup, just as soon as I can.

I use the thing primarily for wood - tried to 'mill' a piece of aluminium but couldn't stand the noise, as the router just isn't intended for it.

I would be right chuffed to meet with you though I live in Phuket and very rarely travel to Bangkok. Could we establish email contact? I'm geoffprobes AT gmail.com
Geoff

[transtar]

Originally Posted by geoff p Hi Transtar, You're right, your machine is a lot more substantial than mine! I actually use timing-belt drives for each of X- and Y-axes but a gear drive on the Z, primarily because I had them in the junk box. The former are ~about~ one to one but the Z is geared down 2:1 then drives a 5/16UNC threaded rod. In Phuket it is near impossible to obtain all metric 'stuff' so I use what is available and let the software do the conversions as required. I'll put up some sketches of my setup, just as soon as I can. I use the thing primarily for wood - tried to 'mill' a piece of aluminium but couldn't stand the noise, as the router just isn't intended for it. I would be right chuffed to meet with you though I live in Phuket and very rarely travel to Bangkok. Could we establish email contact? I'm geoffprobes AT gmail.com Geoff

Now that you mentioned that your drive are via timing pulleys and gearing for Z-axis. Any special advantage on using this method cos I literally tearing whatever hair left on my head to decide on direct or geared drive!

I intend to use my machine basically for milling of thin wood with some ocassional plastic project thrown in.

As for meeting me in Thailand, I can always fly to Phuket for a short holiday with my other half prior hoping a plane to Bangkok! I suppose it will do wonder for my health in the kind of working envoirment I am currently facing in Singapore. Anyway, my next msg to you will be thru email. My email is pokcp@singnet.com.sg

Cheers

[BALLSCREWPRO]

Hi Transtar,
We are from the red dot of the world map. You can come to me and i will loan you
stepper motors and drivers to test your machine before you purchase somethings that do not match your system.
Cheers
ballscrewpro