marker pen driven over an 8x4 sheet help.

**Danny** · 06-11-2011

Ok im going to summarize the parts so far.

Im building a wooden constructed belt driven plotter using these parts from:

http://www.ebay.co.uk/itm/CNC-Kit-3-...item2a14d75139

i need to choose the correct belt size as in width i take it i can use smaller belt for
the shorter Y and wider for the longer x ...say 10mm / 25mm?
15 tooth pulleys ok?

Are these steppers man enough?

http://www.ebay.co.uk/itm/CNC-Kit-3-...item2a14d75139

3M pitch belt driven with 15 tooth pulley gives you 45 mm of axis movement per revolution of driving pulley. Reducing it further 5x gives you 9mm/rev. Driving it with stepper (after reduction) @1/2 step (400 steps/rev) gives you 0.0225mm resolution. I think its enough for your boat drawing or even for cutting
Driving it directly with 15 tooth pulley @1/2 step will give you 0.1125mm resolution

**JAZZCNC** · 07-11-2011

Originally Posted by Danny

Ok im going to summarize the parts so far.

Im building a wooden constructed belt driven plotter using these parts from:

http://www.ebay.co.uk/itm/CNC-Kit-3-...item2a14d75139

i need to choose the correct belt size as in width i take it i can use smaller belt for
the shorter Y and wider for the longer x ...say 10mm / 25mm?
15 tooth pulleys ok?

Are these steppers man enough?

http://www.ebay.co.uk/itm/CNC-Kit-3-...item2a14d75139

These links don't show up for me.?

Regards pulley size I really wouldn't use 15T see post #21 for reason why.! . . . Belts are great but there are some things that must be done correctly or premature belt wear leading to failure is very easy. . .These things are: 1: Correct belt width appropriate to load 2: Correct pully size regards Tooth engagemant 3: Alignment 4:Tension

**Danny** · 07-11-2011

Thanks Jazz sorry for the dumb questions its getting a little clearer to me bit by bit, yep those Ebay links have gone now ill hunt down the Seller and try and find a new one, looking at the shaft coming off of these steppers there must be a way of connecting the pulleys?

**JAZZCNC** · 07-11-2011

Originally Posted by Danny

Thanks Jazz sorry for the dumb questions its getting a little clearer to me bit by bit

Don't worrie one bit about Asking Dumb Q's I for one fully encourage it and pritty much sure they'll have been asked before.!!

Originally Posted by Danny

looking at the shaft coming off of these steppers there must be a way of connecting the pulleys?

When you buy pulleys most often they have just a pilot bore in the centre and come with a Boss on one side. This Boss is drilled & tapped, often in 2 places, then a grub screw inserted which clamps to the motor shaft which often have a flat on one side, if not it's a good idea to grind a small flat your self. The centre pilot bore is then machined to suit the motor shaft.

You have to be carefull regards motor shaft length and the thickness of the motor mounting plate.? If the plate is too thick you won't have enough shaft sticking out the other side.
Often with steppers you'll find the shaft is realtively short so doesn't allow the shaft to pass all the way thru the pulley.? one way to get round this is to either machine away the boss or turn round the opposite way then drill between the teeth for the grub screws. If done this way you must ensure the grub screw is below the surface and no sharp edges from drilling & tapping other wise it will damage the belt.

If Machining pulleys etc is a problem just ask.

These pics may help.?

**Jonathan** · 08-11-2011

Originally Posted by JAZZCNC

This Boss is drilled & tapped, often in 2 places, then a grub screw inserted which clamps to the motor shaft which often have a flat on one side

I'll add it's a good idea to put a small brass bar in the tapped hole between the grub screw and motor shaft as the brass, being a bit softer than steel, will stop the motor shaft getting marked/burred. If you don't it can cause problems trying to get the pulleys off. I would also threadlock the grubscrew to stop it working loose.
Brazing rod is a handy source of brass bar the right diameter...I just part off lots on the lathe then try and find them.

**JAZZCNC** · 08-11-2011

Originally Posted by Jonathan

I just part off lots on the lathe then try and find them.

Your a sick sick boy or sadist not sure which.:rofl:

Belt hole punch pliers and thin brass sheet is much easier.:whistling:

**Danny** · 01-12-2011

After much deliberation i have finaly come to the conclusion that i should be building a router first that will take up to 8 x4 sheets an then have a pen attachment, so am willing to increase my budget accordingly , i have a simple vid for you guys to giggle at , tell me your thoughts! im thinking of running the belting round the entire H frame and am looking for suggestions to how to fix the H frame to while allowing x y movement. http://youtu.be/6QkyB0GB6Ok

**JAZZCNC** · 01-12-2011

Hi Danny,

I think you'll find the cost of belting will make using looped belts of this length un-economical. You probably won't find made up looped belts of this length unless large and expensive widths so will need continous belt with connecting plates. Last price I got for a good quality belt was £12mtr, there are cheaper but when it comes to belts you don't want cheap-O otherwise your in for a world of pain.!!
If plan on driving direct from pulleys off the stepper their will be a couple of issues.

1st Resolution will be low so some reduction will be needed, thou not massive if your just plotting.

2Nd The belt tension required over this length will put very high lateral loads on the stepper causing premature wear. Better if you drive direct from shafts with bearings at either end then drive the shaft with small belts under low tension to the steppers, this will also make it easier to create the reduction.

I would give Rack & pinion a look, I think you'll find it works out just as cheap with less hassle and much stronger if you ever want to upgrade and use it as cutting router.