[eloid]

what the best standard configuration for helicial rack and pinion
i here there are much more robust, quiter and dont skip out.

want to use 7.2:1 gear box with 1810 oz-in motors, but need help calulating
my acceration forces etc.

where to get a helicial rack and pinion locally ( burlington ontario) or online from?

[Tig]

eloid,

Check out ATLANTA Drive Systems
http://www.atlantadrives.com/racks.h...FRVlYQodOEJHog
They are World Leader in Rack & Pinion Drive Technologies specializing in precision rack and pinion, and precision helical gearboxes.
I found them to be very helpful with any sizing questions I had.

[eloid]

eloid,

Check out ATLANTA Drive Systems
http://www.atlantadrives.com/racks.h...FRVlYQodOEJHog
They are World Leader in Rack & Pinion Drive Technologies specializing in precision rack and pinion, and precision helical gearboxes.
I found them to be very helpful with any sizing questions I had.

what did u end up using ie size type etc

[eloid]

I noticed them a lot of metric racks available
what is a good common metric size to use.

[vacpress]

eloid... you need to specify much more information. your machine could be a tiny thing or a huge thing. you mentioned large motors... the size of rack is directly related to the weight of the object it is moving, and the forces that are expected to be put upon it.

[eloid]

4x8 table.... weight ..of gantry only in design stage... guess 150-200 pounds
all steel fram for gantry, riding on a linear bearing set.....
using (dual) 1810 oz-in motors for x axis not sure if im going to switch servo yet..

[Tig]

eloid,
Sorry for the delayed response. As stated by Vacpress, It is very much machine specific. If you give the sales and support people the specifics of your proposed machine, such as a realistic mass to be moved, expectation of rapids, cutting speeds under load, etc., they will be pleased to help you in matching the gear and rack. Don't under estimate the weight of the gantry and any future upgrade of the spindle motor. Gears are expensive you only want to purchase them once.
Keep us informed as to your progress.

[vacpress]

eloid - that sounds reasonable.

ive used a axyz gantry machine about that size that ran on rack and pinnion. i dont know the exact details, but it was pretty heft pieces of metal. the racks were about .75" wide and .5" tall. the pinions which were run by 1 motor with friction belts, an axle through the gantry horizontal beam, and a spring loaded tensioner to hold them against the rack were about 1" diameter.

if i recal, the thing has medium sized nema34 motors and imported looking driver boards - like the larger stuff at keling. this machine could move 350IPM or more, but at these high speeds on a 48x48 it was sort of rediculous and the thing would shudder.

i know that dosent answer your question, but hopefully it helps.

[eloid]

eloid,
Sorry for the delayed response. As stated by Vacpress, It is very much machine specific. If you give the sales and support people the specifics of your proposed machine, such as a realistic mass to be moved, expectation of rapids, cutting speeds under load, etc., they will be pleased to help you in matching the gear and rack. Don't under estimate the weight of the gantry and any future upgrade of the spindle motor. Gears are expensive you only want to purchase them once.
Keep us informed as to your progress.

want to know how to calculate rapids and cutting speeds and speeds under load?
for a rack and pinion design with a gear box, Looking for some advice with the type / sizing on the pitch on the rack

[vacpress]

gear boxes are expensive and have backlash.. the commercial routers ive seen use big belts on 1/2" or larger rods to reduce.

also, 'helical rack and pinion' isnt exactly what you need. regular rack and pinion will be fine. if you use gearboxes as mentioned, helical gear boxes have less backlash, but also often add a 90degree bend.. but really, unless you have a good hookup for some nice gearboxes, why go through the trouble? mxl pulleys are industry standard, easily replaceable, comparably inexpensive, etc. very little backlash, easy to tension! so many advantages.

what do you mean how to calculate rapids? first, rack and pinion is fast. the ratio you need to calculate everything is driven by pinion size.

say you have 200step/rev motors, 4x microstepping = 800seps rev, say you reduce this down 4 times back to 200 step/rev. ok. now say this is driving a 1" pinion, each revolution will move the machine the pinions circumfrence, which is diameterx3.14 so, 3.14!" - imagine! this means that you have a resolution of 3.14inch/200steps = .0157 resolution, but not accuracy as you are using 4x microstepping. the accuracy will be the motor accuracy, parallelism of everything, right down to the runout on the spindle.

this was a simple example, i realize you want much higher accuracy, etc.

Here is good news, the speed! with the above example, lets say your stepper can reliably do 400RPM under full cutting load. 400RPM x 3.14 inch/rev Hah. 1256ipm! not bad, eh!

Using a horizontal shaft and belting instead of 2 motors will save $ over a driver board and motor. it sounds more complex, but it looked simple the times ive seen it..

someone please check my math.
http://www.mcmaster.com/
http://pergatory.mit.edu/2.75/softwa...and_Pinion.xls

may help

[eloid]

gear boxes are expensive and have backlash.. the commercial routers ive seen use big belts on 1/2" or larger rods to reduce.

also, 'helical rack and pinion' isnt exactly what you need. regular rack and pinion will be fine. if you use gearboxes as mentioned, helical gear boxes have less backlash, but also often add a 90degree bend.. but really, unless you have a good hookup for some nice gearboxes, why go through the trouble? mxl pulleys are industry standard, easily replaceable, comparably inexpensive, etc. very little backlash, easy to tension! so many advantages.

what do you mean how to calculate rapids? first, rack and pinion is fast. the ratio you need to calculate everything is driven by pinion size.

say you have 200step/rev motors, 4x microstepping = 800seps rev, say you reduce this down 4 times back to 200 step/rev. ok. now say this is driving a 1" pinion, each revolution will move the machine the pinions circumfrence, which is diameterx3.14 so, 3.14!" - imagine! this means that you have a resolution of 3.14inch/200steps = .0157 resolution, but not accuracy as you are using 4x microstepping. the accuracy will be the motor accuracy, parallelism of everything, right down to the runout on the spindle.

this was a simple example, i realize you want much higher accuracy, etc.

Here is good news, the speed! with the above example, lets say your stepper can reliably do 400RPM under full cutting load. 400RPM x 3.14 inch/rev Hah. 1256ipm! not bad, eh!

Using a horizontal shaft and belting instead of 2 motors will save $ over a driver board and motor. it sounds more complex, but it looked simple the times ive seen it..

someone please check my math.
http://www.mcmaster.com/
http://pergatory.mit.edu/2.75/softwa...and_Pinion.xls

may help

thanks
from what im told helicial racks are not much more money... gear box will be
home made pulley and timing belt..

[Greolt]

I think if you are constructing your own belt and pulleys reduction drives you will rue the day you got helical cut rack.

The side to side movement of the pinion needs to be extremely well constrained.

You will need some quite complex engineering to do this with your motor mount / reduction assembly. I hope you're up to it.

Greg with a capital g

I hope admin quickly ditch this ridiculous idea of making everything lower case.

[eloid]

I think if you are constructing your own belt and pulleys reduction drives you will rue the day you got helical cut rack.

The side to side movement of the pinion needs to be extremely well constrained.

You will need some quite complex engineering to do this with your motor mount / reduction assembly. I hope you're up to it.

Greg with a capital g

I hope admin quickly ditch this ridiculous idea of making everything lower case.

I was planning to make a gear box simmular to this set up
dont see much issues with it

[Greolt]

OK my mistake. I thouht you were going for rack and pinion rather than helical cut gear reduction to drive ballscrews.

You will still have some issues ataining zero backlash between the gears but it won't be as complex as I talked about.

Greg with a capital G

[Greolt]

thanks
from what im told helicial racks are not much more money... gear box will be
home made pulley and timing belt..

Eloid I gather you are not sure which way you're going. Nothing wrong with that. This is a good place to learn.

I recommend you go with one of the design concepts that have been shown to work. There are many examples represented within these forums.

When you start to talk about things like helical cut gear rack, there are complex engineering considerations to achieve minimal to zero backlash.

Leave the more complex engineering problems for the future.

Greg with a capital G

[eloid]

no, no Im planing to make a gear box like above, or something simular with timing belts with the 7.2:1 reduction then driving a rack for the y axis
for 4x8 table, Not sure what rack style or pitch yet

24 dp (diametral pitch), at least 18 teeth on the pinion; but perfer 30 teeth for better number of teeth in contact. Spring load the pinion into the rack
Set my pivoting point for the above mechanism so that it falls on the pitch line of the rack. anyone have some pictures of there setups?

I have question ....servomotors or steppers for a 4x8 table? x and y?
What is most common for larger tables?

[Greolt]

no, no Im planing to make a gear box like above, or something simular with timing belts with the 7.2:1 reduction then driving a rack for the y axis
for 4x8 table, Not sure what rack style or pitch yet

OK just forget about using helical cut rack.

Go with Module 1 or whatever the imperial equivalent is.

Greg

[lgalla]

Helical rack and pinion put extreme side forces on bearings.I doubt the motor bearings could handle the load.Use straight cut gears.
Larry

[jcc3inc]

Gentlemen:

A good source of rack is

www.stdsteel.com/gear.htm

They make various rack; I prefer 24 DP, but they stock 20DP, 20 degree PA,1/2 x 1/2 x 6 feet at about $23.20 ea in qty = 2.

Pinions can be gotten from Boston Gear and Martin gear and sprocket.

Somebody asked for pictures. A couple are attached.

Regards,
Jack C.

[lgalla]

MSC Direct also has Boston gear with pricing.
http://www1.mscdirect.com/cgi/nnsrhm
Larry