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  #1  
Old Tue 23 February 2010, 12:39
albertoslayer
Just call me: albertoslayer
 
san blas
Mexico
Rack and pinion question

Hi

I want to know if the rack 200010 from http://www.stdsteel.com/gr_stock.htm can work with the spur gear 5172T12 Steel 20 Deg Pressure Angle Spur Gear, 20 Pitch, 20 Teeth, 1" Pitch Dia, 1/2" Bore, THE SPUR GEAR IS FORM MCMASTER, thank you, sorry for my bad english

Kind Regards

Alberto
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  #2  
Old Tue 23 February 2010, 19:40
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Yes, they will match each other
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  #3  
Old Wed 24 February 2010, 17:41
Trekker2010
Just call me: Trekker
 
Kuala Lumpur
Malaysia
Hello,
I am very dumb! about this "rack and pinion" thing. I am sourcing the parts that I want to use for my planned MM project. Can anyone please tell me what pinion size I will use to mate the M1 rack? I am buying a set of rack and pinion and i am provided with this information for the pinion: "24 or 30 teeth pinions, 1 module, with 20 degree pressure angle, the inner hole 8mm, and thickness is 15mm. I have very little clue which one to choose. do I specify the overall outside diameter of the pinion I need? Any kind of advice is very much appreciated. Thanks.
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  #4  
Old Wed 24 February 2010, 18:29
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Trekker,

all the information can be found in the forums. At least read this Driving Mechanisms: Rack/pinion, gears, screws, belts & chains

24 or (corrected teeth number) 30 teeth decision partly depends on what motors your planning to use and if it's going to be used with or without gear reduction.
The 8mm inner hole doesn't sound right for a nema34 stepper motor. After you bough or know what stepper you are going to use, you can tell your supplier the inner whole. Expect something in the range of 14mm. Thickness of 15mm sounds right for module 1, if my memory serves me correctly.

If you talk to your supplier then explain him what it's for, often he can also help you out based on application.

Ries
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  #5  
Old Wed 24 February 2010, 19:20
Trekker2010
Just call me: Trekker
 
Kuala Lumpur
Malaysia
Ries,
Thanks for your guidance. I have to do reading to get more knowledge. I will use a NEMA34 motor with 14 mm shaft Diameter, so this I sorted out now, that I need the inside hole diameter on my pinion to match this shaft.
I am still confused on one thing. If I use a 24-teeth pinion with 14 mm inside hole diameter, what is the outer overall diameter of this pinion? Are there different diameter sizes that I must choose?
Again thanks a lot for any advice and responses.

Best Regards,
Trekker (still in the stage of figuring out these new stuffs)
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  #6  
Old Wed 24 February 2010, 19:45
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Trekker,

honestly I am not a mechanical man, so I just told my provider I needed a 24 teeth, 14mm inside hole module 1 rack/pinion. Based on that and the application they created 'something' for me The overall diameter of the pinion can be calculated by the supplier based on the matching rack.

If you are interested, here is a good explanation : http://shopswarf.orconhosting.net.nz/spur.html

Ries
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  #7  
Old Wed 24 February 2010, 20:15
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
You can very seldom buy the correct inside hole diameter from a catalog. Typically the catalog inside holes are small, or even no hole at all. Standard practice is for the customer to enlarge, or create, an inside hole that will suit their shaft.

The 1 module defines the size of a tooth, and if the gear must get 24 teeth of a defined size, then this fixes the outside diameter. A 1 module tooth uses 3.1416 millimeter of circumference.
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  #8  
Old Wed 24 February 2010, 20:28
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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Gerald,

I always have a hard time explaining things, correct wherever I am wrong, or delete my post (Or Mike...) I was lucky I think because my supplier makes them per request. So I could just told them exactly what I needed.

Ries
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  #9  
Old Wed 24 February 2010, 22:12
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ries, you do quite a good job of explaining things, do not underestimate yourself!
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  #10  
Old Wed 24 February 2010, 23:37
Trekker2010
Just call me: Trekker
 
Kuala Lumpur
Malaysia
Gerald,
Thanks again for these information that I gather from this forum. I'm learning stuffs that seem new to me.( I never really cared about these gear things before, on how they work). Now one less confusion is out from my mind.
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  #11  
Old Thu 25 February 2010, 08:06
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
My machine started with 1-inch pitch diameter pinion gears (20-tooth in my case). The motors were direct drive with no belt drive and no gear box. The motors supplied just under 600 oz*in holding torque (4.24 N-m). That combination worked well. The motors could drive the pinion gears properly. The motors did not miss steps. The problem was that each stepper pulse moved the motor too far and the direct drive motors had 'chatter'.

Those motors/drivers required 1,000 steps per revolution. So PI / 1000 = 0.0031416 inches per stepper pulse.

I later retrofitted the machine with geared motors (7.2:1) and replaced the 1-inch pitch diameter spur gears with 1.5-inch pitch diameter spur gears (30-tooth). Those motors/drivers also use 1,000 steps per inch. Doing the math shows that 1.5 inch X PI = 4.7124 inches per revolution. 4.7124 inches / 7.2 gearing = 0.6545 inches of axis travel per motor revolution. 0.6545 axis travel / 1,000 steps = 0.0006545 inches of movement per step.

Many MechMate builders use one of three motor drive systems:

1. Direct drive (no gearing)
2. Belt drive (3:1 to 4:1 gearing)
3. Gear box (7.2:1 is the most popular)

I haven't done my homework with the metric system, so I'll use the three most popular inch sizes, i.e. 1-inch (20-tooth), 1.25-inch (25-tooth) and 1.5-inch (30-tooth). If you use metric, make the necessary adjustments. Many MM builders also use Geckodrive stepper drivers which use 2,000 steps per revolution, so, doing the math for each system using three different pitch diameter spur gears gives the distance in inches per step pulse followed by the steps per inch, i.e. Inches Per Step :: Steps Per Inch:

Direct drive

1-inch pitch diameter: 0.001571 :: 636.62
1.25-inch pitch diameter: 0.001963 :: 509.30
1.5-inch pitch diameter: 0.002356 :: 424.41


Belt Drive (4:1 ratio)

1-inch pitch diameter: 0.000393 :: 2546.48
1.25-inch pitch diameter: 0.000491 :: 2037.18
1.5-inch pitch diameter: 0.000589 :: 1697.65


Gear Box (7.2:1 ratio)

1-inch pitch diameter: 0.000218 :: 4583.66
1.25-inch pitch diameter: 0.000273 :: 3666.93
1.5-inch pitch diameter: 0.000327 :: 3055.77

As you look at the figures, you'll see that as the gear ratio goes up, the distance per step goes down and the steps required to move an inch goes up. Keep that in mind when you dream of high speed jogging. If you want an axis to jog at 15-inches per second and you have a 7.2:1 gear box, you would have to supply 15 X 3055.77 = 45,835 pulses per second with a 1.5-inch spur gear! If you used a 4:1 belt drive and a 1.5-inch spur gear, you would only need 25,464 pulses per second.

There is a trade-off with every method.

I personally prefer the belt-drive system. It gives very good resolution, full torque, i.e. no limitations because of the components used by the manufacturer in the gearbox, and good speed at moderate pulse rates, BUT it is bulky and it requires you to build your own belt-drive transmission.

The Oriental Motor geared motors take away the mess of building your own belt-drive. Those motors are relatively inexpensive (at least to those of us living in the United States where we can buy the motors directly from Oriental Motor) and they perform very well.

Also, don't forget the physics involved. A larger spur gear requires more torque to move the same load. Automatically deciding to use a 1.5-inch spur gear may require more torque that your motor can produce. In other words, a 1-inch spur gear with a 300 oz*in motor produces 600 oz*in of holding torque (remember that the radius of the spur gear is only 1/2 inch). If that motor could barely move the axis with a 1-inch spur gear without missing steps, it could only move 67% of that load if it had a 1.5-inch spur gear (1.0 / 1.5 = 67%). On the other hand, if the motor can easily move the load with the 1.5-inch spur gear then that axis will move 150% faster with the larger gear (1.5 / 1.0 = 150%).

Using that logic (and some practical experience), it follows that you should probably use at least a 600 oz*in motor for non-geared drive systems. You should use at least a belt-drive if you use 450 oz*in motors. You will probably require some kind of gearing with a 300 oz*in motor. Of course speed and cut depth could be reduced so that a small motor could still be used without gearing, but that would compromise production.
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  #12  
Old Thu 25 February 2010, 08:27
KenC
Just call me: Ken
 
Klang
Malaysia
Trackker,
Don't get overwhelm with the spur gear selection, we can buy S45C module 1.0 spur gear off the shelf in most hardware store & they are affortable (RM20~40 depending where). I would suggest experiment with the spur gear after you get your MM built, that what I planned to do. Sourcing the best deal for the racks is more challenging.
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