# 9x20 Rack Alignment Issue



## spanish249 (Dec 13, 2020)

Hello everyone, first time posting here. I recently purchased a 9x20 Chester lathe, as near as i can tell its an exact copy of the Grizzly, Jet and HF lathes.
It is in pretty decent shape apart from an issue with the apron gear that meshes with the rack.

As i move the carriage towards the headstock the gear starts to 'slip'. Upon closer inspection it seems the gap between the gear and the rack increases as it approaches the headstock.

There is a noticeable difference in the gap between the top of the rack and bottom of the ways. I measured the distance from the top of the ways to the bottom of the rack at each retaining screw that holds the rack. At the leftmost screw the distance is 31.3mm (1.232 inch) and the rightmost screw is 32.1mm (1.263 inch)

Im wondering if anyone else has came across this particular issue and might be able to offer some advice.


----------



## Eddyde (Dec 13, 2020)

Hum .031" difference, certainly enough to cause noticeable slop, Most likely was made that way, I doubt the ways wore out that much. I would remount it, maybe replace it as well, that one looks pretty worn.


----------



## markba633csi (Dec 13, 2020)

Yes the factory mounted it incorrectly, one of those "Friday" jobs.  You can approach it a couple ways.  Probably I would remove the rack then spray out the holes with brake cleaner. Epoxy screws into holes. Cut off flush with the bed.  Redrill one mounting hole on each end, intersecting the repaired holes.  Tap holes.  Re-mount rack and mark and drill remaining holes.  Tap remaining holes and reassemble.
-Mark


----------



## spanish249 (Dec 13, 2020)

I took off the rack and inspected it. Cant see any obvious wear, measured it and theres only 0.1mm  (0.003") difference in the size top to bottom.
However the tapped holes that the rack screws go into seem to be misaligned, higher up on the spindle side, lower down on the tailstock end


----------



## C-Bag (Dec 13, 2020)

Welcome to the wonderful mystery world of the Chinese made 9x20 lathe where anything can be wrong. Those of us who have them have decided they are a “kit” and as such it’s up to us to find and cure the problems. And an opportunity for creative repair  I sometimes find things that were originally a design flaw, but often just a one off “made on Friday/Monday” kinda thing. 

I would bet either the rack was drilled wrong for the locating pin or the lathe frame was drilled wrong. I would pull the rack and check it for wear and distortion. You might be able to turn it around if it’s worn. It might also be possible to shim it up and reinstall.


----------



## spanish249 (Dec 13, 2020)

markba633csi said:


> Yes the factory mounted it incorrectly, one of those "Friday" jobs.  You can approach it a couple ways.  Probably I would remove the rack then spray out the holes with brake cleaner. Epoxy screws into holes. Cut off flush with the bed.  Redrill one mounting hole on each end, intersecting the repaired holes.  Tap holes.  Re-mount rack and mark and drill remaining holes.  Tap remaining holes and reassemble.
> -Mark


Ya i think that might be the way to go mate, im not sure if the rack is supposed to be flush with the bottom of the ways or that there is a certain gap that should be allowed


----------



## DavidR8 (Dec 13, 2020)

These is just a random thought...
Could you shift the rack toward the headstock maybe .5" or so to allow you to drill and tap all new holes?


----------



## spanish249 (Dec 13, 2020)

DavidR8 said:


> These is just a random thought...
> Could you shift the rack toward the headstock maybe .5" or so to allow you to drill and tap all new holes?


Ya thats a good idea, id probably shift it towards the tailstock end though so im not losing any travel with the apron


----------



## Cadillac (Dec 13, 2020)

Maybe mount a scribe on the carriage run it back and forth to give yourself a reference. Pull the rack off file and oblong the mounting and locating holes. Then when in the proper position drill some new holes to hold in its new place.


----------



## spanish249 (Dec 13, 2020)

Cadillac said:


> Maybe mount a scribe on the carriage run it back and forth to give yourself a reference. Pull the rack off file and oblong the mounting and locating holes. Then when in the proper position drill some new holes to hold in its new place.


I may do that, unless anyone who owns one of these lathes knows what the gap between the apron gear and rack is supposed to be?


----------



## Cadillac (Dec 13, 2020)

Full engagement without bottoming out the teeth. Try and run a piece of paper between the gear and rack that will be plenty clearance.


----------



## benmychree (Dec 13, 2020)

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.


----------



## spanish249 (Dec 13, 2020)

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


----------



## markba633csi (Dec 13, 2020)

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


----------



## RJSakowski (Dec 13, 2020)

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.


----------



## spanish249 (Dec 13, 2020)

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.


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


----------



## RJSakowski (Dec 13, 2020)

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.


----------



## spanish249 (Dec 13, 2020)

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


----------



## savarin (Dec 13, 2020)

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.)


----------



## savarin (Dec 13, 2020)

check out this site if you havnt seen it before


			Steve Bedair's 9 x 20 Lathe Page


----------

