9x20 Rack Alignment Issue

Full engagement without bottoming out the teeth. Try and run a piece of paper between the gear and rack that will be plenty clearance.
 
I'd think there should be a clearance from the top of the pinion teeth to the bottom of the rack teeth of about .020", not easy to measure --- but if you bottomed the teeth out and then moved the rack up that amount, it should be OK.
 
Checked the screw holes in the rack, theyre drilled about 0.5mm (0.019") out of line with each other from one end to the other. Also checked the rack for flatness, its bent inwards in the middle
 

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Post #10: What matters is the mesh of the gear and rack; you ideally want about 75% engagement or thereabouts. Use the gap as only a jumping off point, but make sure the plane of the rack follows a point on the apron perfectly at both ends of the bed without lift or drop
 
I would check the pinion gear and its bearing for wear first. The gear should not be jumping out of engagement with the rack. If ythe gear is worn, replace it first.

Rather than drilling and tapping new holes, I would elongate the existing holes in the rack. This can be done with a rat tail file. To properly seat the the cap screws. you will most likely need to elongate the counterbore as well. This is best done on a mill with an end mill. With care, it could be done with a drill press.

To properly set the rack clearance, I would mount the rack with the two end screws and use a shim pack to adjust for the right clearance in the center of travel. Then I would measure the distance from the top of the ways to the bottom of the rack at that point. That will be your dimension for locating the rack. Seat the remaining screws and check for proper position at each screw point. Tighten the screws securely and either enlarge the existing holes for the next size larger roll pins or drill new holes. If enlarging the existing holes, I would place shims above the hole locations to prevent the bias from moving the rack.
 
RJSakowski said:
I would check the pinion gear and its bearing for wear first. The gear should not be jumping out of engagement with the rack. If ythe gear is worn, replace it first.

Rather than drilling and tapping new holes, I would elongate the existing holes in the rack. This can be done with a rat tail file. To properly seat the the cap screws. you will most likely need to elongate the counterbore as well. This is best done on a mill with an end mill. With care, it could be done with a drill press.

To properly set the rack clearance, I would mount the rack with the two end screws and use a shim pack to adjust for the right clearance in the center of travel. Then I would measure the distance from the top of the ways to the bottom of the rack at that point. That will be your dimension for locating the rack. Seat the remaining screws and check for proper position at each screw point. Tighten the screws securely and either enlarge the existing holes for the next size larger roll pins or drill new holes. If enlarging the existing holes, I would place shims above the hole locations to prevent the bias from moving the rack.
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I checked the pinion gear, no visible wear, its not that its jumping out of engagement, its more that the rack is not perfectly parallel with the bed and is closer to the bottom of the ways at the headstock end so that the gap between the pinion and rack increases as the carriage moves to the left and is only barely meshing
 
Sorry, I interpreted "starts to slip" as jumping teeth.

If the pinion gear is good then I would just proceed with aligning the rack. With the roll pins out, you may be able to push the rack close enough without any modification. Just insert the proper shim pack above the rack to get the proper engagement with the pinion.
 
Ive just tried that now, had to leave out the roll pins and the two centre screws but the gap above the rack is even now. Ill eventually fill those two tapped holes and re-drill so its fully secured. Thanks
 
The amount of play in that gear rack with the drive wheel is very pronounced.
Remove the screws and check if the roll pins hold it in the correct spot.
The rack can bend/flex quite a ways.
If I remember when I aligned mine I left the pins out and the hole clearance for the screws was sufficient to get it into full mesh and alignment.
If not then just re drill and tap the holes a tad further along.
When I get to the shed today I will check mine for you.
I'm one of those who purchased the lathe full well knowing it was a kit of parts.
(Ahh, answered too late.)
 
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