Not sure I'm ready for this - I've started building!

[Mike F]

Finally got my pulleys

I ordered them through www.sdp-si.com at a cost of $136, approx 72 GBP, just a little better than the 413 GBP quoted over here!!! However, there was a little sting in the tail as the postage, advertised as "Freight amounts to be determined using standard published list rate." , turned out to be $69. I am still a happy bunny though as the total cost was still just about a quarter of the original quote. It certainly pays to shop around.

I ended up getting 3 x 16 teeth, 3 x 32 teeth, 1 x 48 teeth pulleys and 3 x 60 teeth belts - all are GT2 specification as recommended here. The 48 teeth pulley is to allow a 3:1 reduction on the X axis if the 2:1 gives whipping problems on my 2000mm ballscrew.

I could not get the bores I required so will have to bore these out to suit. One of the ballscrew, 32 teeth pulleys will need a sleeve but should not be a problem.

At last I can start working again.

Mike

[10bulls]

Originally Posted by Mike F Finally got my pulleys...

This is all a bit over my head at the moment, but from what I can make out, you are going with the GT2 belts based on a trade off of backlash versus cost.

Originally Posted by arvidb ...First, they recommend the AT tooth profile with polyurethane belts to get minimum backlash. If I understand correctly, HTD is worst in this respect, followed by T, GT, and AT, in that order.

For my design I was considering going with the T2.5mm profile 6mm wide stuff that rswww sells. For a similar shopping list to yours, this would come out around £56 ex VAT. These would be more than ample spec for my bodgy design. Is the GT - T difference that great or are there other considerations?

BTW - great looking machine!

[Mike F]

10bulls

I too was very confused by the huge number of different spec belts and pulleys, hence my questions to the zone. As far as I can make out, the reason GT are so good is the profile of the teeth, they are rounded giving much quieter operation. I don't know whether I have gone over the top by specifying 15mm belts but that decision seems to have been supported here by others.

Reliance, a company in the UK, offer backlash free versions of GT pulleys but these are the ones they quoted me silly for (£413) Obviously there is a very real cost consideration here.

I have yet to get the motors mounted so cannot comment yet on how well the system performs but they look pretty good and I cannot distinguish any backlash when fitted over the pulleys by hand. Incidentally, Jeff Davis who supplied my servo motors, says he uses standard pulleys and belts and has no problems with backlash.

I have seen your thread but cannot recall the size of your machine. Mine is fairly large which is why I went for the 15mm x 5mm pitch belts but 6mm x 2.5mm pitch seems awfully small, but there again, I'm a beginner too so what do I know??

Mike

[Mike F]

I am now at the point where I really do have to make the decision between Rutex and Gecko. Although price is not a fundamental issue I still do not want to pay more than I need to. As I see it, the advantage of Rutex is that I, as a complete electronic moron, can simply buy a mother board and IO board and plug it into the system. On the other hand, Geckos are cheaper but require a third party IO board and home/limit switch board.

Now the question. Bearing in mind my total incapacity for all thing electronic, how easy is it to interface Geckos with the necessary gizzmos for home/limit switches and IO functions such as spindle, coollant etc.? Is there something I can simply plug in?

Mike

[coherent]

Mike, If you've made it this far I don't beleive the Geckos will be a problem. Go take a look at the PMDX breakout boards at http://www.pmdx.com/ .
Something like the PMDX120 should do everything you need and has all of the pinout/in connectors and relays built on the board. You can set things to your softwares preferences (like pulled low or high, charge pump settings, etc) There are other brands so look around and read the manuals (PMDX has them online for download). They will make connections a snap.
I only mention PMDX because I have one and am happy with it.
-marc

[ger21]

Also llok at this breakout board. http://www.campbelldesigns.com/

[Mike F]

Marc & Gerry,

like pulled low or high, charge pump settings, etc

This is what is worrying me - I don't understand the terminology so don't know exactly what I will need but thanks for the replies, I will be investigating the sites suggested. I just hope they cater for electronic dunces

Mike

[ger21]

The high or low are software settings, not a big deal. The charge pump is a safety circuit that basically keeps your motors from spinning when the software doesn't have control yet.

The breakout boards really make setting up Geckos (or Rutex) drives almost plug and play.

[HomeCNC]

Mike, Take a look at this guys products for Break-out-boards and charge pump board. He sent me a full set of his products to test. He is also working with Art and the Mach 2 software for full compatability with it.

http://www.cnc4pc.com/

[JavaDog]

Originally Posted by HomeCNC Mike, Take a look at this guys products for Break-out-boards and charge pump board. He sent me a full set of his products to test. He is also working with Art and the Mach 2 software for full compatability with it. http://www.cnc4pc.com/

Nice price on that board. Think it'll be comparable to the PMDX board?
Gotta let us know how the testing goes!

[coherent]

Most software like Mach 2 will let you select either pulled active low or high, so it's not a big issue except that if it's not built into the board and you manually wire it, you need resistors and a specific voltage to pull the pin(s) high or low. Basically, the software is either reading a low or high voltage at a specific pin as either active (on) or inactive (off) and just does whatever the software is programed to do (like turn a spindle on with an M3 g-code) when the active signal changes from low to high or high to low.

Charge Pump is simply a software safety feature that will work with any software that will send a signal via the parallel port (normally pin 17). If for any reason the software driving your machine burps, bumps, locks or quits (windows error, power bump, driver error whatever) it makes an emergecy stop and the breakout board stops all motors, turns off all the relays etc. It's a very nice safety feature.

The reason I choose the PMD over Campbells was it had the relays built in and avoided the cost of additional "daughter boards" or wiring relays.
I think PMD 120 board has 4 a/c relays to power things like spindle for on/off, coolant pump for on/off or whatever you want. You only have so many pins available for stuff like limit/home switches and relay output signals. Doesn't matter what breakout board, as you are limited by the 25 pins per parlallel port and only so many allow signals in and so many allow signals out. Any board will basically do the same thing, but others may have 1 or more relays built on. Mainly breakout boards keep things isolated from your computer motherboard LTP port and ensures that you don't damage your computer when a problem occurs with a driver board (and visa versa). You can also get a cheap PCI multi I/O card that will give you another LPT port effectively doubling available pin in & outs. Of course if you do that you may need another breakout board to use that ports effectively also. That way you could use a number of limit, home or reference switch setup alternatives. For example I'm currently setting up a plasma table with a torch height controller and a torch height sensor and since I already have a number of limit and home switchs connected, I required more pin in/outs than one parallel affords. You'll have no problem setting up/wiring the stuff you're talking about... and the cost is minimal compared to motors, drivers, linear bearings and the like... the hardest part will be running the wires and mounting the switches! (sorry for the long post and blabbing on about stuff you may already be aware of, but hope it helps a little)
-marc

[Mike F]

To all those who have recently replied - many, many thanks. I am so glad I found this site after contemplating a self build. Unfortunately my mechanical skills far outweigh my electrical skills and, as I have said previously, I will be leaning heavily on the good, patient, expertise here.

Marc - long winded or not, it was just what I needed and I am sure it is probably not the first time you have explained this detail. Thanks. If I want both home and limit switches on a three axis machine plus spindle and coolant, does this mean I need to occupy eight additional pins of the parallel port? If so are there that many available to me without the added complexity of another parallel port?

Presuming I will be using Mach II or III, does the software give me enough control to negate the need for limit switches and thereby save the need for using pins I probably haven't got? The small Isel machine we have at the moment has no limit switches, you just tell the software what the cutting limits are.

Jeff - When are you likely to be able to report on the CNC4PC boards?

So, bottom line is that there is definitely something out there that is comparatively idiot proof that can just be plugged into Geckos to do the necessary additional functions other than driving the motors. That being the case it looks like Gecko may well be getting a sale.

Mike