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  #1  
Old Mon 04 December 2006, 12:53
DocTanner
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Checking Parts List confirmation of pinion & gearbox

Ready to order a few of the expensive parts. Looking for opinions to see if this is a workable system.

4 Oriental Motor PK296A1A-SG7.2 $257.00 each
http://catalog.orientalmotor.com/item/stepping-motors--1068/pk-series-stepping-m otors/pk296a1a-sg7-2?&plpver=11&origin=keyword&by=prod&filter=0

4 Geckos G202 $134 each www.geckodrive.com

http://www.martinsprocket.com/gears.htm#
3 Spur Gears Catalog Number TS2035BS 1/2 35 tooth
1 Spur Gear Catalog Number TS2020BS 1/2 20 tooth
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  #2  
Old Mon 04 December 2006, 23:06
Gerald_D
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The motors and drives look good, but the gears have to be matched to racks as well. (Also had problems finding those specific gears in their catalogues - gave up knowing that matching to racks is more important)
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  #3  
Old Tue 05 December 2006, 01:11
Gerald_D
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Have just seen that you have already purchased your racks "4 - BF200011 20dp 20 degree 6' racks $23.20 each" (link)....let me try and figure out martinsprocket's catalogue again..
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  #4  
Old Tue 05 December 2006, 03:34
Gerald_D
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The gear pinions look good as well, but I have a bit of a problem with the "large" 35 tooth. The motor plates will have to swing further down to accommodate the diameter and I will have to check the effects on the laser-cuttings (slots in the gantry ends and spring lengths). Nothing too serious if you have already ordered those plates, but we could improve the aesthetics and get the motors level if we wanted to.
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  #5  
Old Tue 05 December 2006, 06:57
Mike Richards
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DocTanner,
I've just done the math on your selection and I'm wondering why you selected such a high gear ratio. The 35-tooth gears have a pitch diameter of 1.75-inch, so 3.14 X 1.75 = 5.495 inches of travel per revolution. The motors require 2,000 X 7.2 = 14,400 steps per output shaft revolution. That means you will end up with resolution of 0.00038-inches per step, or approximately 4/10,000. For all practical purposes I would expect actual resolution to be almost an order of magnitude less, somewhere closer to 0.004-inches, or approximately 4/1,000. (Please don't think that I'm assuming that you can't build a machine that will hold tight tolerances. What I assuming is that to build a machine that can consistantly be accurate to 0.004-inches, which is about the thickness of a piece of copy paper - or half the thickness of a human hair, would take substantial effort.)

Going back to the numbers, depending on your pulse generator, you might have a maximum speed of around 3-ips (Mach3 running full out on a PC, which is about 45,000 steps per second). The 3.6:1 gearbox would give you twice the speed, and for all practical purposes, the same resolution.
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  #6  
Old Tue 05 December 2006, 08:26
Gerald_D
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Mike I didn't see a big issue with DocTanner's selection because:
a. 3.6:1 gearboxes with 20 tooth pinions are supposed to be very good with Mach3
b. 7.2:1 gearboxes are said to have no more backlash than the 3.6:1 gearboxes
c. bigger pinions run smoother and last longer
d. 3.6 / 20 is exactly the same as 7.2 / 40 and 35 teeth is not much less than 40 teeth

Maybe my assumption a. is wrong? Are the Ascension guys running bigger pinion gears?
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  #7  
Old Tue 05 December 2006, 08:46
DocTanner
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Thanks Mike and Gerald

Mike,
I picked these items after doing a lot of reading your post of your over at shopbot. Always paying particular attention to yours and Gerald's and and a few others'posts.
http://www.talkshopbot.com/forum/mes...312/14311.html

Quote "I agree with your suggestion for a 5:1 to 8:1 gear ratio if using Mach3/Gecko/Steppers. If I went that route, and used a 30-tooth spur gear rather than the standard 20-tooth, I would end up with a top jog speed of about 20-ips with the 5:1 box and a top jog speed of about 12-ips with the 8:1 box (assuming 45,000 pulses per second from Mach3 and the Geckos set to 2,000 steps per revolution)."

I'm easily confused
DocTanner
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  #8  
Old Tue 05 December 2006, 09:00
Mike Richards
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Gerald and DocTanner,
I've got egg all over my face. Somehow my math was completely wrong. When I refigured it on my usual calculator, an HP with RPN, the results were totally different than the results that I got with a TI, using standard algebraic entry. (That shows that an old dog really can't learn new tricks.)

Here's the math, assuming Mach3 running full out at 45,000 pulses per second:

45,000 pulse per sec / 2,000 steps per rev = 22.5 revs per sec
22.5 rev per sec / 7.6 gear ratio = 3.125 output shaft revs per sec

1.75 pitch dia X 3.14 = 5.495 inches traveled per gear rotation
5.495 X 3.125 = 17.17 max ips

So, whatever method I used to figure things the first time was totally wrong. DocTanner should get single axis speeds as fast as he is comfortable using with the parts that he has selected. Multi-axis speeds may be a little slower, but still faster than my Alpha.

Edited: My first calculation should have had something like 0.00038 X 45,000 to get the maximum speed.
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  #9  
Old Tue 05 December 2006, 09:27
Gerald_D
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DocT, have you placed an order for 10 20 454 PC yet? I could quickly do you a special for those 35 tooth pinions?

Mike don't worry about the egg - getting your face dirty is as pleasant as getting your hands dirty!
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  #10  
Old Tue 05 December 2006, 09:38
DocTanner
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Thanks Mike. I'm out of my league on a lot of the electronic side of things. Your opinion is highly valued.

Gerald, YGM

Doc Tanner
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  #11  
Old Tue 26 December 2006, 15:22
Brian_B
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Hi Gerald,

I was following the above discussion regarding maximum speed attainable as a function of gearing ratio and pinion size. The tradeoff between the resolution/torque of a geared stepper motor and positioning speed makes for a real head scratcher.

If you are building a straightforward CNC router, you might be able to make use of a higher jogging/positioning speed, but your cutting speed isn't going to change all that much unless you step up to a much more powerful spindle and a hold down system to handle the increased forces.

On the other hand, if you're looking at building a laser cutting system, speed is more limited by laser power and substrate. Substrate holding is almost a non-issue (especially if you're like fabrica and working with multi-ton slabs of granite!).

It appeared that the upper limit on speed while using geared steppers might be more limited by the number of pulses per second the control software can generate. Mach III is limited to 45,000 hz. Are you aware of any software packages that go higher than this? I have been trying to find out what Quantum is capable of, but haven't seen much about it yet.

I suppose that raises several other questions. Let's say we design a system using 7.2 geared steppers, a 1.75" diameter pinion, but with 100,000 pulses/sec and 2,000 pulses per revolution - following the calculations above that would give us a max speed of 38.16" per second or 2290" minute - about 27% faster than the ShopBot Alpha's rated top speed.

So my questions are related to the top speeds that the various components of the system can withstand. How many pulses per second can the steppers handle (Gecko 202's can get up to 200Khz)? And what is this speed likely to do to the MechMate itself in terms of structural integrity, accuracy and repeatabity?

Brian
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  #12  
Old Wed 27 December 2006, 06:37
Mike Richards
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Geared motors from Oriental (PK296A1A-SG7.2, PK296A2A-SG7.2) are limited to 250 RPM. So 250 X 7.2 = 1800. 1800 / 60 seconds = 30 revolutions per second. 30 revolutions per second X 2000 pulse per revolution = 60,000 steps per second maximum. Torque at that speed looks to be about 80 oz*in. compared to a maximum of about 700 oz*in. (Oriental motor has charts for all of their motors.)

When the G100 is ready for use, it will give you plenty of speed. But, Mach3, at 45,000 pps, isn't bad.
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  #13  
Old Wed 27 December 2006, 17:43
Brian_B
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Mike,

Thank you for the explanation. After reading your last post and integrating it with the torque/speed curves on Oriental's website, I have a much better understanding of the relationship between all the various components.

I suppose my interest in considering the use of the 7.2 ratio geared stepper is less to increase torque than to improve resolution. As our machines may ultimately be limited in that regard by accumulated errors in its construction, the use of such highly geared steppers will probably prove to be wishful thinking at best.

My interest in high speed operation is more for the use of flying optics to direct the beam of a CO^2 laser. As the cutting "tool" never contacts the substrate - at least in the sense of a router bit cutting a sheet of plywood or MDF - the needed torque can be relatively low, but should be coupled with a positional accuracy of around 0.005" - the width of the laser beam when passed through either a 2" or 4" focusing lens.

I was obviously trying for high resolution, by using the 7.2 geared stepper, as well as high speed, by using a larger pinion gear and high rpms. While I realize there are tradeoffs as there must be some inverse relationship between the two, I thought I would give it a try!

Perhaps it would be best to compromise by going with a 3.6 geared stepper, a somewhat smaller pinion and keeping the rpms under 150 and thereby working within the limitations of Mach3.

Depending on the features and capabilities of Quantum, it may be possible to alter the characteristics of the machine via software if not by changing out pinion gears at a later time.
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  #14  
Old Thu 08 February 2007, 21:49
reza forushani
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Can someone give me the model on Mcmaster.com for the pinion 20 teeth. I cannot seem to be able to find the right one.
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  #15  
Old Thu 08 February 2007, 22:12
Gerald_D
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McMaster-Carr 5172T12 will fit directly onto the 1/2" shafts of most of the Oriental Motor stepper motors:

"Steel 20 Deg Pressure Angle Spur Gear 20 Pitch, 20 Teeth, 1" Pitch Dia, 1/2" Bore" you will need to drill & tap 2 grubscrew holes in each.

These pinions must run on the following racks:

"Part No. 5174T21 : Steel 20 Deg Pressure Angle Spur Gear Rack 20 Pitch, 1/2" Face Width, 1/2" Height, 6' Length" or equivalent


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  #16  
Old Fri 09 February 2007, 00:19
reza forushani
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Would they work with rack BF20001 from stdsteel?
Is there a spur gear that I don't have to drill?
Thanks for your help
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  #17  
Old Fri 09 February 2007, 00:35
Gerald_D
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I think you mean rack BF200011 from stdsteel. Yes, that is okay.

I don't believe you will get a catalogue drilled pinion anywhere - let a mechanic/machinist friend help you drill & tap the threads.
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  #18  
Old Fri 09 February 2007, 05:22
DocTanner
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I ended up using these from www.daltonbearing.com Spur gears with 2 set screws.
Part number YSS2020 $21.90 for 20-Diametral Pitch 20°-pressure angle 20 tooth spur gear 1/2
And $29.49 for part number YSS2035 for 35 tooth.
A bit higher priced than some of the other suppliers, but a no hassle way to get finished.


DocTanner
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  #19  
Old Fri 09 February 2007, 05:35
Thomas M. Rybczyk
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Reza,

Martin Sprocket and Gear http://www.martinsprocket.com/home.htm carry a 20 tooth 20 degree pitch spur gear the part number is TS2020BS and it has a screw set.

I use these with my 1/2 inch shaft direct drive 640 oz Keling motors with no problems.

Look under products, gears then open the pdf catalog, select Spur Gears 20? from menu. Then it's on page 8 at the bottom.

Only problem is you cannot buy direct from them, but if you call them they will give you the location of the nearest distributor to you.

Good Luck,
Tom
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  #20  
Old Fri 09 February 2007, 09:15
reza forushani
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thanks everyone. I am almost done ordering everything hopefully. We will see I am sure I need some other things. Now just waiting for everything to come in and get started building. I will report my progress. Thanks for all your support.
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  #21  
Old Fri 09 February 2007, 11:06
Hugo Carradini
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In have all my contacts ready except for the rack and pinion. I haven't had an answer and I tried more then 5 Companies. I will tried a couple more and ask for some help if I have no success.
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  #22  
Old Fri 09 February 2007, 11:53
Gerald_D
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I am surprised at the luxury you guys have to get pinions ready bored and set-screwed. Under these conditions, one should be even more careful to get the part numbers absolutely correct.

1. Be sure of your motor shaft diameter. The sizes of 0.5", 12mm, 13mm, 14mm have all been mentioned for various motors. They are all different and are not interchangeable.

2. Determine the number and orientation of flat spots on the motor shaft. Make sure you have a grub/set screw on each flat spot. A single screw on a shaft with two flats is not enough.

3. Do not tighten a set-screw against the cylindrical part of the shaft - you will disturb the accuracy of the shaft and there is a good chance that the pinion will permanently damage the shaft if you then try to remove it. (The shafts are relatively soft stainless steel, for magnetic reasons)

4. Use MechMate drawing M2 30 110 T as a guide. There it is said the wall thickness can go as low as 3.5mm with twin grubscrews. Which means a 20 tooth DP20 pinion can go on a 14mm MotionKing shaft even though the gear guys say you shouldn't bore that gear over 0.5" (Their next size is 9/16", but 14mm is still smaller than 9/16")

5. If you have the luxury of ready-made gears, I suggest you go all the way and get the supplier to harden them as well.
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