# Quick Change Gear Box Conversion Questions



## Strtspdlx (Jun 15, 2015)

I'm looking to convert my th54 to a qc54 from my understanding with a new banjo and forward reverse lever I can install it. My question is will I need anymore gears for the drivetrain and will I need to replace me lead screw or will my existing lead screw bolt directly to the gear box? 


Regards-Carlo


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## wa5cab (Jun 15, 2015)

Carlo.

First step is to determine which model of QCGB you have or are going to buy.  1500 (3/4" leadscrew) or 1700 (5/8" leadscrew) has a tumbler with a spring loaded pin similar to the ones on the two settings levers.  6800 has a tumbler with an arced slot.  A stud sticks up through the slot and a nut on the stud locks the tumbler in position.  Once you've determined that, go to  Downloads > Machine Manuals, Catalogs & Drawings > Atlas/Craftsman/AA > A/C Lathes > A/C Lathe Accessories and download the appropriate manual.  Be sure to read the description.

The leadscrew does not bolt to anything either on the TH or on the QC machines.  It has a keyway milled on the left end which when you slide the leadscrew into either the FWD/REV gearbox or the QCGB engages with a key in the hole.  The conversion requires cutting 1" off of the left end of the leadscrew but you do use the original leadscrew.  Use the parts list to be sure that what you buy includes all of the parts you will need.  The drilling template shown on the parts drawing is probably always missing but fortunately is only needed with the 1700 (5/8" leadscrew).  I haven't studied the parts list and compared it to the 10F parts list to see which gears are already on the TH.  If you don't have the TH parts manual, download that as well.


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## Strtspdlx (Jun 16, 2015)

Well it's either a 1500 or 1700 gearbox as it has a spring loaded lever for the tumbler. I contacted the seller to ask what size the bore is that the lead screw goes into. Hopefully he'll be able to give me an accurate measurement I have to measure mine when I get home as I haven't the first clue which it has. 


Regards-Carlo


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## Strtspdlx (Jun 16, 2015)

Also I went to downloads and it will not allow me to download anything it says I do not have permission too. I'm on my mobile phone using tapatalk. When I get home I'll go on my laptop and see if it allows me too then. 


Regards-Carlo


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## wa5cab (Jun 16, 2015)

Carlo,

On all of the 10" and all of the 3/8" bed and most of the 1/2" bed 12", the diameter of the left end of the lead screw is 5/8".  Atlas apparently did this so that they wouldn't have to change the 10" FWD-REV gearbox or the left lead screw support on the 12":.  In any case, as your machine is a 10F it doesn't matter whether the gearbox was originally sold as a 1500 or a 1700.  You won't need the drill template and you should have the stud gear (16/32 compound gear).  However, it wouldn't hurt to have a newer one, although it probably still won't have the thin steel disk between the two gears.  I think that first appeared in the late 1950's and the 6800 replaced the 1500/1700 circa 1950 or 51.

On your Downloads access problem, my understanding is that access to Downloads is restricted to Active Member and above, which seems to require first getting past 30 posts and then having an Admin tic the box that says you are also a member of that Group. This would be indicated by a blue bar with Active Member in it at the left of your posts under your avatar (which currently shows a "?").  Look at some of the other threads and you will see examples.  This apparently doesn't happen automagically so I'll post a not to the Admins asking one of them to tic the box.

In the meantime, if you'll send me a PM with your email address, I'll send you the PDF on the 1500/1700.


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## Strtspdlx (Jun 16, 2015)

According to the seller the bore in the gearbox is 3/4" so I'm assuming it's a 1500 gear box so should my lead screw measure 5/8" which according to the information at hand it should. I believe my machine is pre 1950. Am I Interpreting this correctly? 


Regards-Carlo


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## Strtspdlx (Jun 17, 2015)

I didn't get a chance to measure
My lead screw last night. More or less I completely forgot. I think I'm gonna take a chance and see if I don't get lucky with the lead screw sizing. If anything I may have to make a bushing or turn my lead screw down and broach a new key way  in it. 


Regards-Carlo


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## wa5cab (Jun 17, 2015)

Strtspdlx said:


> According to the seller the bore in the gearbox is 3/4" so I'm assuming it's a 1500 gear box so should my lead screw measure 5/8" which according to the information at hand it should. I believe my machine is pre 1950. Am I Interpreting this correctly?
> Regards-Carlo



Sorta but not exactly.  To repeat, the lead screws on all Atlas 10" and all Atlas/Craftsman 12" built prior to 1968 are 5/8" diameter on the left end.  Prior to about 1939 or 1940, they were 5/8" overall except for the right end where a short part is 1/2" dia.  From then up until 1967, the majority of the length was 3/4" with only a short stub on the left end still being 5/8".  These later ones are commonly referred to as 3/4" lead screws, despite the 5/8" dia. stub on the left end.  

The obvious reason for why Atlas did things this way was to avoid having to make two different versions of the 10" FWD-REV box, 12" left bearing support, and various QCGB's.

I have to assume that the seller mis-measured the bore of the output shaft as all of the Atlas and Craftsman QCGB's except for the pair produced from 1968 on have a 5/8" diameter hole with internal key on their output.


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## Strtspdlx (Jun 17, 2015)

Okay. I really appreciate your help. I did purchase it and expect for it to arrive around the 25th. I can finally begin making the parts to restore my machine. So long as it works I'm very excited I have a big
List of things I'd like to make most of which require threading. 


Regards-Carlo


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## wa5cab (Jun 17, 2015)

You're welcome, and good luck.  See slight revision above.


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## wa5cab (Jun 17, 2015)

And BTW, you should now have access to Downloads.


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## Strtspdlx (Jun 18, 2015)

I do now have access. It won't download on tapatalk so I just signed in on my mobile internet and it worked fine. I think tapatalk is beginning to be more of a pain then it is helpful. 


Regards-Carlo


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## wa5cab (Jun 18, 2015)

That sounds normal.  Tapatalk doesn't seem to work with anything.except another Tapatalk user.


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## Ronaldo (Jul 8, 2015)

So If my machine has a 3/4 lead screw is it safe to assume that it was built after 1968?


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## wa5cab (Jul 9, 2015)

No.  The first Atlas lathe built with 3/4" dia. lead screw came out in 1938, the 10F, followed in 1940 or late 1939 by the 101.07403.  There were no changes in 1968.  The final Commercial versions appeared in 1967.


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## Strtspdlx (Jul 15, 2015)

If anyone has a 40 tooth change gear for an atlas 10" they'd be willing to sell please let me know I can't seem to find one right now. 


Regards-Carlo


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## Strtspdlx (Jul 16, 2015)

Just for S&G I threw a 54 tooth gear on the machine to make sure the box works without binding. It is suprisingly quiet considering the amount of wear. And I set it for 4tpi and tried to thread. I knew going into it that it wouldn't cut the right Amount of threads with my current gearing. But it did cut some threads. Something like 9tpi. 
	

		
			
		

		
	





Regards-Carlo


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