Dowelling a Metric Gear Rack

[LoFe]

Hello,

I have a very simple rack and pinion system. One rack is driven by a pnuematic cylinder which drives a pinion keyed to a shaft. On the same shaft is another keyed pinion that drives the second rack. The start and end position of the 2nd rack is critical, therefore the OEM dowelled and bolted the racks to the carriers that bolt to the linear bearings.

The issue I'm having is reverse engineering the location of the dowel hole. The racks are both module 4 one rack is 370mm long and the other is 580mm long. The problem is the begaining and end of the rack are not on the center or end of a tooth. I can get any critical dimension from a CMM I just don't now how to properlly dimension a print for a machine shop. I'm assuming I need to pick the center line of a tooth and use it as a primary datum.

If anyone could offer any advice or examples I would appreciate it.

 

[tr1ntx]

A sketch or drawing would probably lead to a better answer.

"The problem is the begaining and end of the rack are not on the center or end of a tooth."

Are the beginnings or ends of the 2 racks the same distance from the center or end of a tooth? I guess another way of saying that is "are the racks cut the same?"

Measuring the distance from the beginning or end of the racks to the center or end of a tooth, is that an whole number? Or a logical fraction such as .75? If so, it is probably intentional. If not, the OEM used some other datum to align the racks. You'll need to figure out what that datum was, or if an alternate one can provide the necessary accuracy.

The situation could be that the 2 racks (in raw form) were aligned in a fixture using a wide pinion spanning both their widths, then one end was just arbitrarily cut flush. Then possibly the dowel holes were drilled and the racks were cut to final length. Look at the distance from the end of the racks to the nearest dowel hole. Is it the same one end of each rack? (or both ends possibly)