Timing Pulley Sizes Question

[CoffeeRich]

I am now aware that I will need pulley setups for all of my axis on my HF mini with a HobbyCNC 200oz kit. Does anyone out there know what size pulleys I will need for getting more torque out of the setup? I can get the pulleys pretty cheap through mcmaster but Im not really sure where to start as far as the diameters to get this thing to be nice and solid when milling metal. I am using the stock screws on the x and y but have a PHD ballscrew slide on the z. Any help would be greatly appreciated.

Rich

[Runner4404spd]

i would probably use around 3:1 reduction to start.

[Nono]

Maybe 4 to 1 But I think start with 3 to 1 also. Try http://www.grainger.com
They are cheaper than mcmaster and carr. When you figure it out let me know

[LongRat]

CoffeeRich,
have you tried the setup direct drive? I only ask because I am considering the same setup and thought that the reduction drive idea would give negligible benefit, because of the reduced torque of the steppers at higher RPM - which they will be doing on a reduction drive.

[CoffeeRich]

I already tried to do it direct drive and the X and Y seem to skip around when the bit is cutting anything harder than HDPE.

A smaller drive pulley on the motor and a large pulley on the screw should at all points in the RPM range increase the amount of torque. You do get some loss of torque but it shouldnt be noticable. Im not sure on the numbers but I would guess that the pulleys setup like that should increase it by at least two fold. Im just going by all my previous experience though.

Anyone have actual numbers right now? I Will be able to sit down and figure them out after fireworks time here.

[LongRat]

Ok, that's good information to have given that you have tried it. To see that increase in torque you will of course lose rapid speed by a similar factor. I think I might look into 640 oz.in steppers and Gecko 201s in that case, possibly also applicable to larger machines if I upgrade too. What do you think of this?

[CoffeeRich]

The rapid speed on it wont suffer that much though because of the speed that it has now if I crank it up. Im not so worried so much about speed. Im way more worried about it missing steps. I will eventually upgrade to servos with encoders and geckos or something like that. I plan on ordering pulleys tonight and will hopefully have them mounted by weekend if nothing else comes up.

[MikeAber]

CoffeeRich,

I am running 2:1 reduction on my mini gantry mill with 200oz steppers and 5mm pitch ballscrews to get an effective 10 tpi. My rapids run about 55 IPM without missing steps. When cutting 6061 or 7051 I can run about 20 IPM and anything in steel (light cuts .025 or less) I must slow down to 5 - 10 IPM. I find that this is adequate for my needs as I am just a hobbyist. I am using 14 teeth on the stepper motor and 28 teeth on the lead/ballscrew with XL series pulleys and 1/4" drive belts. Make sure you have or file a flat on the shafts for the setscrews, you will be sorry if you don't.

Mike

[RotarySMP]

I'm running 9mm wide HTD belts with Al pulleys 2:1 (48 tooth and 24 tooth) and 167 InOz steppers on my mini lathe. My Z rapid (4mm pitch metric acme screw with nylatron nut) is good for about 30IPM on the parts if the bed which are not too tight.

The stock lead screws are rather fine aren't they (2mm pitch?) Going to a 4:1 reduction will likely be very slow. somewhere in the 2 or 3:1 range is a better compromise.

Your lead screws are likely to be around 25-40% efficient. A ballscrew is around 95% or higher, and gives the huge advantage of backlash control, plus a coarser pitch.

Changing from a direct driven 2mm lead Acme to a 3:1 reduction driven 4mm lead ballscrew (assuming a near linear stepper torque curve, and enough voltage) should give you a speed increase of 3x to 6x and enough torque ( ~3X) to never loose steps while cutting within this machines limited structural abilities.

[hoagiem]

have you tried lapping the ways on your x-y axis? i checked the gib on mine while doing the lapping and was suprised at the contact pattern on the gib strip, or lack there of. it took a while but the gib shows even wear and both axis glide smooth. i am also using tetra lube grease, it made quite a bit of difference. if you haven't tried it yet you might go that route before investing the time and money masking an existing problem.

[RotarySMP]

Mine is a lathe. The problem with the minilathe bed is that it is not of even thickness. I will address this when I strip the machine down to fit the ballscrews (just maling the bearing blocks).

I did lap the cross slide, and it make a huge difference on these chinese kit set tools.

I haven't been able to source a small supply of way oil here, so I just use Mobil 1. Although the machine is on the balcony there has been no rust at all in two years.

[hoagiem]

ooops, that post was meant for coffeerich. not used to this forum. good luck with your lathe.