3 Axis CNC router

[JoeHarris]

OK, I have introduced my initial ideas on the intros thread and already received some really useful pointers.

The plan is (after some advice from you guys!) to build an aluminium framed 3 axis 1500x1000mm CNC router driven by 2no. ball screws on the x axis. In order to drive the 2 ball screws on the x axis I intend to use timing belts, linking them to a single stepper motor.

The ball screws will be either 2005 geared up or 1610. So far I am thinking 2005 because of the potential whip issue over such a large distance.

Having decided to go down the HTD timing pulleys/belts route for connecting my steppers to the screws I have a few querys I hope someone can shed some light. Please excuse my ignorance! - I'm here to learn.


My questions are:

01 which belt width / pitch would you recommend for this application?

02 I am unsure as to how the pulleys will be attached to the stepper / ball screw - do you have any photographs, technical manuals or just a description of how this can be achieved?

03 Is the lateral pressure on the screw and motor shaft likely to cause damage to the bearings?

03 If I mount the steppers through 20mm alu plate will this allow enough length in the motor shaft to connect it to the pulley? if not is there a way of extending the shaft?

04 in order to adjust/maintain tension on the x-axis drive system I intend to use idler pulleys - how do the bearings work for these pulleys?

any images people have of successful arrangements would be really useful as I try to move the design of my machine along.

Thanks in advance!

Joe

[Web Goblin]

I would go for a 5mm pitch 16mm or 20mm wide belt. The pinions can simply be drilled and tapped to accept a grub screw to fix it to the shaft or you could use these : http://uk.rs-online.com/web/p/locking-bushes/4888062/ They are a bit expensive but are really good and are easy to adjust and set the pulley on the shaft in the correct place. Personally I dont like attaching the pinion directly to the motor. The shaft can easlit be extended and supported by and extra bearing or two. If you have a look at my build you can see how I extended the Y Axis motor assembly. This might give you some ideas. You can extend the shaft via a coupling or using a solid bar bored out to take both shafts. An idler pulley is simply for tensioning as you say. Mount it on a sliding block with a bolt for setting the tension with a locking nut to secure it once set. What do you mean by how do the bearings work for the idler pulleys?

Ian

[Jonathan]

1)I'd use 5mm pitch 15mm wide belts:

http://www.bearingstation.co.uk/prod...iming_Belts/5M

2) Just a grubscrew is generally fine.

3) No

3 again) Probably not. I generally mill a pocket out of the 20mm plate leaving 4mm or so for the motor to rest on yet still be well supported by the thicker material outside. Bit difficult if you don't have a mill though. You can extend the shaft, but it's a lot of extra parts and expense that shouldn't be necessary.

4) You can use idlers to tension the belt, but it's generally easier to have the motor mount slotted so you can apply tension by pushing against the motor and tightening it down.

Pictures:

[JoeHarris]

Thanks for the replies - I will post some more screen shots when I get some time to progress the design!

[John S]

Don't listen to Jonathan, he's still learning

Use http://www.beltingonline.com/5mm-htd-timing-belts-4575 for belts and pulleys, more choice and cheaper.
good service as well

[Jonathan]

Use http://www.beltingonline.com/5mm-htd-timing-belts-4575 for belts and pulleys, more choice and cheaper.
good service as well

Nice one... bearing station's service has been generally awful. Every order has taken about a week to arrive for me. They post the same way with cheap or expensive service and take ages to despatch so makes no difference. Plus in the last order they sent one wrong pulley and belt. Price is similar for the pulleys but I think I'll not bother with bearing station due to the poor service. I only recommended them before as I thought they were the cheapest.

[JAZZCNC]

Hi Joe,

Sorry not replyed to some of your previous post's where you asked me directly, I've had eye trouble so time on computer has been limited hence me not being around much.!

Others have answered the belt Q's regards width, pitch etc but there are things you need to be made aware about with this size machine.?
One of the things I found when I built my machine was that long belts where not available in 5 x 15mm HTD so depending on the X axis screw centres you may have the same trouble.?
The X screw centre's on my machine are 1300mm using 30T pulleys so needed belt length over 2750mm the longest HTD 5mm pitch 15mm wide I could find was around 2400-2500mm.
The way I got around it was to have them special made costing around £20 each. I bought 2 keeping one for spare, that was over 3yrs ago and I've only recently swapped for the spare and that was because I left a pulley lose after changing ratios from 1:2 to 1:1 for high resolution job and it fell off killing the belt in the process.!!

Regards mounting pulleys you will need the ballscrew ends machining longer than standard so the shaft goes all the way thru the pulley giving better purchase for the grub screws. Also grind a small flat on the shaft for the grub screw to grip and stop the pulley spinning.
Regards idlers and tension then You don't need lots of tension on the belt and infact if you put them under too much tension they wear quicker and it also puts tension on the ballscrew bearings and if Ott can cause binding and possible missed steps.? Just enough tension to stop the belts flapping around and jumping teeth is all thats needed and lightly tensioned idlers is all thats required. (I just use 2 bearings with large penny repair washers for guides)

I'm posting the pics of my well used setup and While my setup looks ugly and is roughly thrown together it's simple, works very very good and accurate with high reliabilty even thou I run it in some of the worst conditions for running belts.!!
I dont have any guards or shields, the machine mostly 98% of time cuts Aluminium with chips flying every where and it has never failed or lost position either thru skipped teeth or missed steps. While It's capable of max rapids around 11mtr/min with 5mm pitch screw 1:2 ratio(effective 10mm pitch) 6Nm Nema 34 motor running 75Vdc I detune it to 7mtr/min which is more than enough for my needs and also why It's NEVER, NOT WOUNCE missed steps or lost position or sync under cutting conditions or rapid movement.

To give you an idea of the resolution and what 1:2(10mm pitch) belts can achive then I've attached the Aztec calender pic with a link to video see the detail better.

Hope this helps and inspires.!

http://www.youtube.com/watch?v=wjDvi...ature=youtu.be

[John S]

How big's that Aztec calender ?

[Jonathan]

How big's that Aztec calender ?

About 150mm.

Here's my attempt with the same G-code:



That was with 1:1 ratio and 10mm pitch screws...

http://www.youtube.com/watch?v=Gh2pjXQY5U8

Wish I could afford to use the 20mm aluminium waiting on my router bed to make a 740mm one!

[John S]

What was that programmed in? Aspire ?
Is it flat, it looks curved ? Giz the code, i might cut this in gold, well brass anyway worth more than gold.