New to rack and pinion, seeking advice.

[Konstantin]

Hi.
I am building a new router with a footprint of 2.5’ x 4,5’ using a PorterCable7518 and aluminum profileslink. I went to check out some rack and pinion prices and options and basically my choice is between MartinSprocket and MartinSprocket, yeah. I have settled on getting 2 Martin Sprocket 6’ racks and it would be enough for X and Y axis, dual on X and single one on Y. Being new to R&P I am not totally certain about what pitch and pressure angle to choose from, I guess I am getting the ½ x ½ (square section) rack.
About the pinion, that pitch diameter is optimal? Some prefer the 1” pitch diameter and use a reduction from stepper to the pinion. What are the considerations here?
Thanks for you input.

[Diane-MooreGear]

Please tell me you haven't bought from Martin yet. I have 20DP-20PA Rack for around $40 and do ship to Mexico.

Diane@mooregear

[Konstantin]

Thanks Diane.
Believe me, 'buying' will be the last step. As of now I do not understand what is the criterion in choosing the rack. If anyone would have the patience to explain what pitch is needed it would be great.
Today I spoke with the martin sprocket sales representative and asked a simple (as it appeared to me) question, what pitch is the rack they sell?
They use numbers like 3,4,5,6,8,10,12,16,20 (link to MS catalog) but what those numbers mean and what units are those? The sales rep could not answer me coherently, he said that the rack pitch is not important, it is the pinion pitch what is important and begun talking about the pitch diameter, but that is another thing.
How can I purchase when I don't understand what I am buying.
Someone please shed some light here.

[ahren]

Konstantin,

You need to get matching pitch (spacing between teeth) and pressure angles (basically the shape of the teeth) between your rack and your pinion gear that rolls on the rack for your system to work. You then choose the number of teeth on your pinion gear to set the resolution of your system -- the larger the diameter, the more you'll move per rotation. For each pitch, there are recommended minimum diameters so that you have more than one tooth engaged with the rack at all times.

Your best bet is probably to go with a proven solution. I might humbly suggest Diane's 20 pitch, 20 degree pressure angle racks coupled with our rack and pinion drive system, which uses 20 pitch, 20 degree pressure angle, 20 tooth gears that work extremely well with it. There are literally hundreds of machines running on this combination in the field right now. The 20 pitch indicates that on a 1" diameter pitch circle, you will have 20 teeth, or linearly, 20 teeth per 3.14159 inches.

Metric rack is typically specified by the space between teeth, so a module 1.5 rack is 1.5 mm between teeth.

Hope that helps,

Ahren
CNCRouterParts

[Konstantin]

Thanks Ahren.

[Diane-MooreGear]

You beat me to it Arhen.

I would add that 20DP-20PA is used most often for a couple of reasons. One: it's readily available as a stock item and Two: it's a good match between the need for resolution and cost effectiveness. Some people do try to reinvent the wheel because they have a special aim in terms what they intend to make with their machines, but it is my understanding that with a combination of rigidity, spring loading pinions into the rack, the balancing of the drive system and smart programming, you can achieve tolerances within +/-.005" (perhaps far better) with the 20DP-20PA Rack.

Diane

[mrosupply]

https://mrosupply.com/category/197-G...%20Gear%20Rack

Here is a list of Boston products regarding Racks & Gears.

Hope this helps.