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birchy
14-03-2011, 11:57 PM
I've recently bought an ex-demo (read as: brand new apart from 2 small chips on paint) Warco WM16 mill/drill for a bargain price of 750. Having weighed up the price of power feed and DRO vs the cost of a CNC conversion, I decided to go CNC.

This is my first ever build, however I've worked in engineering since starting my apprenticeship 19 years ago.

I'd like some help and advice for the build, especially for anyone that has previously converted similar machines such as:

weiss wmd20lv
champion 20v
amadeal ama25lv
warco wm18 (slightly bigger)

After stripping the machine to get it into my cellar workshop I cleaned off all the packing grease, re-lubricated all slides and screws and set up the gibs to be as tight but smooth as possible. For the time being, because the machine is new and because I don't need micron accuracy, I am going to use the stock lead screws and convert to ball screws if/when I need them. To work out which stepper motors I would need, I ran the Z axis in the up direction (as that is the stiffest to turn by hand) using a dial torque wrench. Worst point was near the top and gave me a reading of 1.6Nm. The X and Y axis were <1Nm with a vice and around 5Kg of weight on them. Based on that, I figured that the commonly available 3.1Nm motors would be more than capable, so I bought a kit from Zapp Automation: http://www.slidesandballscrews.com/driver-three-axis-p-621.html via Gary's eBay listings. He had one kit listed as an auction starting at 180. I won it for 205 so had another joyous moment.

Sooo, my questions so far:

1. Have I bought the right kit? I'm pretty sure I've done good as the components in the Hong Kong specials on eBay didn't look very well matched. Plus I wanted separate, easy to replace parts rather than an all in one board.

2. Are 3.1Nm stepper motors man enough? I thought they were double my needs but have read that "holding torque" is not equal to motor torque.

3. Should I go for direct drive couplings or use reduction pulleys and timing belts?

4. The stepper motors are 8-wire. Should I wire them in series or parallel? What's the difference in performance?

5. I've fabricated a custom stand with a couple of shelves, a stainless steel drip tray and castors (for ease of moving the machine around the workshop!) with intentions of adding pumped coolant/suds at a later date. I'm going to build all the electronics, including the PC components, into a control panel box which will be mounted under the mill, on one of the shelves. Is it "normal" to use 4-core cable and 4-pin plugs and panel mount sockets for the motors or is it better to hard wire them through skin top glands, especially if there's suds in the vicinity? Will there be any problems using this setup?

6. Software will be 100% Linux based. I've not used any M$ or Windows products for 3+ years, so don't wish to take a step backwards. I'm a complete newby to CAD but have tried FreeCAD, HeeksCAD, Medusa4 and QCAD. Of these, QCAD was by far the most intuitive, and worked well with dfx2gcode which I then ran in EMC2. Bearing in mind that I want to control 3 axis of my mill, will QCAD be sufficient? I know it's only 2D but can 3D gcode be auto-generated by combining standard orthographic views drawn in QCAD?

Thanks to anyone that can help. :smile:

birchy
20-03-2011, 05:56 PM
Nobody can help? :confused:

m_c
20-03-2011, 09:12 PM
1) Looks like a reasonable kit for starting with, and should be more than up to the job you're asking.

2 & 3) Certainly on the z-axis, I'd be considering a reduction drive, or an extra counterbalance to reduce the weight the stepper is having to lift.
You need to allow for the loads being greater when cutting, and also as you're running the normal leadscrews with their reduced effiency compared with ball screws, it may be wise to run reduction on all axis.

4) Bipolar parallel provides the best match to the drives.

5) I've seen plenty builds where motors are connected via connectors. Main thing is you use good quality ones, that lock in with a high enough rating, and make sure you never unplug them with the drivers powered on (doing so is likely to lead to the drives becoming an expensive paperweight!)

6) Probably best to start a thread in the CAD & Cam Software forum, as I have no idea about linux!

birchy
20-03-2011, 09:37 PM
Thank you for responding.


...as you're running the normal leadscrews with their reduced effiency compared with ball screws, it may be wise to run reduction on all axis.I was looking at possible ways to mount the motors and using belt drives will make life easier. What ratios should I consider? I was thinking of 2:1 reduction on all axis. Or maybe a bigger ratio on the Z?


I've seen plenty builds where motors are connected via connectors. Main thing is you use good quality ones, that lock in with a high enough rating, and make sure you never unplug them with the drivers powered on (doing so is likely to lead to the drives becoming an expensive paperweight!)Was looking at this today and considering I have to join to the wires on the steppers (probably solder and sleeve with heat shrink), I think it will be better to run the cables through PG16 glands and terminate inside my case. For neatness, it might be worth fitting some 35mm DIN rail and 2.5mm terminals, but will have to decide on a case and play around with the layouts. Regarding motor cables, I've seen mention of 1.5mm shielded 4-core. Is that really necessary? Seems like massive overkill for 4.2A drives/motors? I know it's braided and not shielded cable, but would SY cable be ok? http://www.sycable.co.uk/ It has a bit of extra strength and can more take knocks and bends than most shielded cables. And I can get it from work. :wink:


Probably best to start a thread in the CAD & Cam Software forum, as I have no idea about linux!Did that previously but had limited response. I think it's just a case of trying them all until satisfied. Currently trying HeeksCNC and HeeksCAD. They're a bit unorthodox but starting to make sense now.

m_c
20-03-2011, 09:44 PM
The benefit of starting with belt drive, is it's fairly easy to swap ratios at a later date with minimal modification.
2:1 is a typical choice.

I can't comment about anything to do with linux on a home computer, as my limit with it is the command line on webservers!
Perhaps asking somewhere like CNCZone may find more linux cad users?

birchy
20-03-2011, 10:12 PM
As you say, it makes sense to go with belt drives as they can be modified easily if I run into problems at a later date. Also, I want to keep the machine as standard as possible and using belt drives should allow me to use existing mounting holes.

Not too bothered about software at present as I can generate working gcode using either QCAD and dxf2gcode or HeeksCAD/CNC.

I'd also like to utilise the steppers as power feeds for manual machining. Is that possible or even worth bothering with?

EDIT: Regarding the cable selection, I can now see why 1.5mm2 is used. I'd forgotten that DC circuits run bigger currents. http://www.solar-wind.co.uk/cable-sizing-DC-cables.html. Still wondering about SY though? We use a lot of multi stranded SY at work in various sizes from 0.5mm2 upto 10mm2. What is the need for screened cables?

m_c
20-03-2011, 10:40 PM
It probably is possible, but I'd say learning the required GCode to manually enter moves will be far simpler, or just jog the axis at whatever speed you need.

Jonathan
21-03-2011, 12:20 AM
The steppers and drivers you have are the same as mine, and they work well on my milling machine which is about the same size as yours. Only difference is I run them on 75v which gets you higher speed. The power supply could be better - I'd advise getting yourself a toroidal transformer for 70v if you want to get the most out of the motors. Nothing to loose by trying the one you've got first though!

I think belts are a must really. I've not tried direct drive because I think the ability to change the ratio and thus operate the motor in the best torque region is well worth the relatively small amount of money on pulleys. Also I got a heap of pulleys cheap on eBay which always helps!

When I had 1nm motors on my mill I ran them on 3.2:1 (ish) - not very fast at all. Since then I've had the 3nm motors on 1:1 which is plenty fast enough so I've not bothered testing other ratios. Different story for the router though where I used different pulleys on each axis.

I quite often manually machine with the steppers and Mach3. Either by typing Gcode or arrow keys/jogging.

Definitely Bipolar Parallel.

I used CY 1.5mm cable since SY, though available cheaper, is not as flexible. I think it has an extra layer, or thicker, insulation/shielding which makes it less suitable for constant motion.

birchy
21-03-2011, 10:56 PM
Right, I need to buy some pulleys and belts. What sort of pitch should I be looking at and where's the best place to buy them?

birchy
22-03-2011, 01:12 AM
Hmmmm, they're expensive. Maybe I should buy a dividing head (was gonna get one anyway) and make them myself? Where can I find specifications for such things?

Jonathan
22-03-2011, 02:46 AM
Hmmmm, they're expensive. Maybe I should buy a dividing head (was gonna get one anyway) and make them myself? Where can I find specifications for such things?

They certainly are. I used a vertex 6" rotary table and put a stepper motor on it.

Can cut the pulleys quite quickly if you grind a form tool and hold it in boring head, or just make a quick holder as it's not exactly complicated. I've posted a thread with more about it somewhere, including a program I wrote to mill the pulleys. My pulleys are XL so in the end I just ground a trapezium of the right dimensions on the end of a piece of 5/16" HSS from the lathe.

5mm Pitch

birchy
23-03-2011, 12:35 AM
Isn't it ironic how I could do with a cnc mill to make the parts for my cnc mill? I know there's a load of timing pulleys dumped in a box at work. Will have a mooch through it when I get time. I certainly need to buy a rotary table or dividing head. Not really sure whether to get the Vertex HV6 rotary table (http://www.warco.co.uk/HV6-Rotary-table-C32F40EE41.aspx) or go the full hog and get the dividing head (http://www.warco.co.uk/Vertex-Semi-Universal-Dividing-Head-03382F176B.aspx#) or just make my own rotary table with a standard industrial gearbox and indexing via a plate with suitably positioned holes.

I guess timing pulleys could also be made with a home ground broaching tool. First of all, I need to find me a pulley so I can decide the easiest way to copy the profile...

EDIT: B'jaysus, look what I found in me scrap bag. It's a 30 tooth with OD of 93.5mm and 30mm wide. Bit big though. Bummer. We have lots of them at work. Tooth to tooth is 10mm so I assume it's a 10mm pitch?

m_c
23-03-2011, 06:59 PM
Personally I'd go for the rotary table, as it's a bit cheaper.
Remember, you'll still need some method of holding the pulley blanks onto whatever you buy.

Simon C
23-03-2011, 07:36 PM
Birchy, I use thease timeing pullys on my mill conversion http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=182-694 RS generaly arent the cheepest but there service is second to none and delivery is free (normaly next day). i used a 1:4 ratio but im only useing 205 oz-in steppers so your 425 oz-in steppers should work well on the 1:2 ratio you were thinking of useing. i also used the original leadscrews (5mm pitch i think mine are). the max speed i get with my 1:4 ratio is 1800mm/min so its pritty slow but does get the job done. this was only a temporary conversion to help me cut parts for the router/plasma table im makeing. i will buy a new mill with a vertical dove tail colum to do a proper permanant conversion on after i finished my currant project. btw my mill is a Champion mill from chester uk.


Hope this helps

regards
Simon

birchy
24-03-2011, 12:55 AM
Agree on the rotary table as the savings could be spent on a decent chuck and other tooling.

These don't seem too bad on price: http://www.bearingstation.co.uk/products/Pulleys/Timing_Pulleys/Timing_Pulley_5mm
I'm guessing the 16mm wide belt is about right? 10mm seems a bit narrow. Only thing they don't show is the maximum bore size. Any idea what size pulley I can go down to on a stepper with an 8mm shaft? I'm guessing about a 12 or 14 tooth to have some meat for the grub screws?

Simon C
24-03-2011, 08:52 PM
Birchy, I use thease pullys on my mill conversion http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Ne=4294957561&N=4294920273+4294955369 RS usualy arent the cheepest but there service is second to none and delivery is free (usualy next day). I used a 10 tooth on the motor and a 44 tooth on the leade screw (used original leade screws as this was a tempray conversion just to help cut parts for my router build). Im only useing 205 oz in motors and get a max feed raite of 800mm/min so its pritty slow but gets the job done (can get 1200mm/min but sometimes loses steps at that speed). So i think useing your 425oz-in motors runing a 2:1 ratio you should get decent speed and still have enough power. Oh and as for concern about haveing enough "meat" on the hub of the small pulley for your motor i just put a grub screw in the center of the pulley bettween two of the teeth and aslong as you debur the hole propley you wont have any problems with it chewing up the belt. think i taped the motor pully for a M4 grub screw and the leadescrew pully M6. Btw my mill is a Champion mill from chester uk. If your motor shafts are 8mm Dia i would recomend atleast a 12 tooth pully.

I posted on this thread lastnight but it didnt show up, not sure what happend.

Hope this helps

regards
Simon

birchy
25-03-2011, 01:02 AM
Just ordered T5 pulleys and belts in sizes 14 tooth for the motors, 28 tooth for the X and Y, and 42 tooth for the Z. So I have 2:1 on XY and 3:1 on Z. Went with www.bearingstation.co.uk as they have a "price match guarantee" and were cheaper than the trade prices Brammer and RS give the company I work for.

Out of interest, how did you find the accuracy using the standard lead screws?

Jonathan
25-03-2011, 01:13 AM
Might be too late but this site is very cheap for timing belts, lots of pulleys too:

http://www.fish4parts.co.uk/Mechanical.80/Chain-%25252F-Belt-Drives.1094/Belts.10941/Classical-Timing-Belts.109413/

I've got most of my belts from them.

My Vertex HV6 rotary table works well as a 4th axis. I just made a mount for a 1nm motor on to it from a piece of 3" aluminum bar - not difficult to do at all. Wear on the worm drive might be a problem though.

birchy
25-03-2011, 08:23 PM
Might be too late but this site is very cheap for timing belts, lots of pulleys too:

http://www.fish4parts.co.uk/Mechanical.80/Chain-%25252F-Belt-Drives.1094/Belts.10941/Classical-Timing-Belts.109413/Hmmmm, they be very expensive I'm afraid! I paid 3.01 each for T5 x 15 x 14 teeth pulleys and they're 7.76 each on fish4parts. The 42 tooth was 6.94 on bearing station and a whopping 16.69 on fish4parts. Need I say more?


My Vertex HV6 rotary table works well as a 4th axis. I just made a mount for a 1nm motor on to it from a piece of 3" aluminum bar - not difficult to do at all. Wear on the worm drive might be a problem though.I've only got a 3 axis kit at the mo, but the facility is there to add a 4th. I was also a bit concerned about gear wear...that is why I mentioned using an industrial gearbox in a previous post. Rotary table and 4th axis is going on the back burner for now as I have to do!

You didn't mention the performance of your standard lead screws. What was accuracy like and how much backlash compensation did you have to set in EMC?

Simon C
25-03-2011, 09:14 PM
The lead screws on my chester mill have a 5mm pitch i think. As for precision it depends what kinda work im doing, if im just drilling holes in flat plate (basicaly just useing the table to eaqualy space out a row of say 5 holes) i get accurate results but if im milling and puting side force on the cutter accuracy is not so good. im useing mach3 and the backlash comp is set to about 0.13 mm (cant remember exactly), backlash comp is only a last resort and doesnt substitute for a good solid mechanical set up. also the lead screws have 2 ball thrust bearings near the handles and thease dont cope well with the radial force put on them by the belt tension. as i said this was a tempary conversion and just wanted to CNC it as fast and cheeply as poss. you will probly find yourself switching to ballscrews soon after you have done the cnc conversion but no harm in giveing it a go with the standard screws and see how it goes. cool thing with ballscrews is not only the minimal backlash but you only lose about 5% of your motors torque in the nut where as with norm screws you use around half your motors torque just in the friction of the nut/screw.


Oh and the max feed rait i get on my set up is 800mm/min not 1800 as i said in a previous post, musta had my mini lathe in mind when i said 1800


regards
Simon

Jonathan
25-03-2011, 09:20 PM
Hmmmm, they be very expensive I'm afraid! I paid 3.01 each for T5 x 15 x 14 teeth pulleys and they're 7.76 each on fish4parts. The 42 tooth was 6.94 on bearing station and a whopping 16.69 on fish4parts. Need I say more?

I was referring to the timing belts being cheap - not the pulleys!

I'll post more later, busy at the moment.

birchy
25-03-2011, 09:32 PM
They didn't seem to have the belts in the sizes I wanted. My dearest belt was 3.18. Must admit I spent a couple of hours Googling before settling for bearingstation though.