# Changing gears for 1 1/4 TPI and using QC gearbox



## gearhead (Oct 29, 2017)

I'm very new to lathes. I need to wind coils  with my Atlas 12". It has the QC gearbox, but it is only set up to turn as wide as 4 TPI. I have the manual, and it tells me that I can turn 1 1/4 TPI if I change gears on the banjo. I think, if I'm looking at things right, that I currently have a 40 in the A position and a 48 in the C position. (The 40 actually looks like it's in between the A and B position, so I'm not sure about that.) The manual says I need 64N and a spacer F in the B position and a 20N and 64F in the D position, with a 32 compound gear.

Can I get gears and spacers to do this? And is there anything else I need to know before I start combing eBay for gears? Thanks for the help.


----------



## Rob (Oct 29, 2017)

You can also get new gears from clausing for not much more than used ones on EBay.  Amazon also sells Boston gears made from steel that are a direct replacement for the change gears.  The Boston Gear PN's are GB20 & GB64


----------



## gearhead (Oct 29, 2017)

Thanks so much, Rob. What terms would I search on to turn those up on eBay? I did not come across anything like that while looking for "atlas lathe gears." Also, what about that spacer that I need? Is that anything special, or is it just a bushing? Actually, even if it's just a bushing I could turn, I still suck at turning pretty badly and might want one that's already done.


----------



## Rob (Oct 30, 2017)

If you do a search for "Boston Gear GB20" a 20T shows up.  Amazon also has one that is cheaper than the ones on EBay.  I did not see a Boston Gear GB64 on EBay or Amazon.  As I mentioned you can still get the gears new from Clausing.  You can also get a new bushing from them.  When I have checked prices on new gears from Clausing they are just a little more than used on EBay and you will get new ones.  If you look at the spacer it has 2 keyways in it.


----------



## wa5cab (Oct 30, 2017)

It was also common to use the 20T gear as a spacer.  But gear or spacer, both need to have the double keyways.  

Making the bushings takes more than just a lathe as they have double keys on them.

There is a section on coil winding in the MOLO.  And a selection chart in Downloads that will show you which version of MOLO is nominally correct for your model number lathe.  And another document on the history of the MOLO that will tell you which Editions belong to which versions.


----------



## larry4406 (Oct 30, 2017)

Clausing is quite responsive with parts inquiries if you email them at  info@clausingsc.com


----------



## gearhead (Oct 30, 2017)

wa5cab said:


> It was also common to use the 20T gear as a spacer.  But gear or spacer, both need to have the double keyways.
> 
> Making the bushings takes more than just a lathe as they have double keys on them.
> 
> There is a section on coil winding in the MOLO.  And a selection chart in Downloads that will show you which version of MOLO is nominally correct for your model number lathe.  And another document on the history of the MOLO that will tell you which Editions belong to which versions.



Yes, I have the MOLO, and am referencing page 133 of the manual which indicates the gears and spacer I outlined above. I've not done this before, and I'm not sure if I'm reading the chart correctly or where exactly the physical positions of those gears are. I guess I'm just trying to get a good understanding of this before I got ordering random parts that might not fit or ordering them and finding out I still don't know what the heck I'm supposed to do with them. Thanks.


----------



## wa5cab (Oct 31, 2017)

First, there are 10 versions (0 to 9) and 33 editions of the MOLO.  And they are not all paginated the same.  So if giving a printed page number for someone to look something up, you should give the year or Edition (1954 on) or Version (all 1937's).  And if 1937V2 through V5, also whether the page number is from part 7 - Threading or not (Part 7 in those versions starts over at Page 1 and then Part 8 jumps back to what it was in V1).

The A,B,C,D positions are variable depending upon what gears you have installed.  Where the letters are shown on the drawing of the banjo (AKA change gear bracket) is just the rough location.  To load up the banjo, loosen all of the nuts holding the gears on and remove all that aren't going back on in the same letter position.  Then lower the banjo.  To set up the new combination, you should start with the gear that drives the screw gear or the QCGB.  Then the second gear that drives the first.  And so on.  Put several drops of SAE 20 on each stud as you go.  Use a strip of brown Kraft type packing paper or 24# typing paper to properly mesh each gear as you tighten its nut.  When finished, swing the banjo up (with paper strip in place) and tighten the clamping lever (and remove and discard the paper strip).  Also, I would wear surgical gloves as the gears should be quite greasy.  When finished, re-grease the gears before removing the gloves.


----------



## benmychree (May 8, 2018)

That setup could put a fatal strain on your gearing (pot metal) I'd think twice or three times before going down that road.


----------



## Bob Korves (May 8, 2018)

What John York said.  If you are not experienced enough to change the gears, then you have no place trying to do a 1 1/4" pitch thread on your first go 'round.  There are many ways that operation could go far wrong, with the definite potential of breaking and damaging things you really do not want to break or damage.  Atlas gears are also notoriously weak.  Let's start with:  Why do you need a 1 1/4" pitch thread?  Please tell us what you have in mind doing, the longer story...


----------



## Dave Paine (May 8, 2018)

I do not know what the original poster needed, but I have needed to single point external and internal 1 1/4in x 8 tpi threads to make items for my wood lathe.  It seems this thread is common for many wood lathes.   Another common size is 1in x 8 tpi.


----------



## Bob Korves (May 8, 2018)

Dave Paine said:


> I do not know what the original poster needed, but I have needed to single point external and internal 1 1/4in x 8 tpi threads to make items for my wood lathe.  It seems this thread is common for many wood lathes.   Another common size is 1in x 8 tpi.


The OP is trying to cut 1 1/4 TPI, not 1 1/4" diameter, per his post.  A VERY coarse thread.


----------



## benmychree (May 8, 2018)

Dave Paine said:


> I do not know what the original poster needed, but I have needed to single point external and internal 1 1/4in x 8 tpi threads to make items for my wood lathe.  It seems this thread is common for many wood lathes.   Another common size is 1in x 8 tpi.


You misunderstood what was proposed, the proposition was to cut a 1-1/4 threads per inch LEAD, not 8 threads on a 1-1/4 inch diameter part as you suggest.
This sort of thing is possible, but highly questionable on such a lightly built machine with pot metal gearing (and other parts) I have done such jobs, but mine is a 19" swing lathe with iron and steel change gears and no pot metal.


----------



## kd4gij (May 8, 2018)

The OP is talking about winding coils not gutting threads. To wind 1 1/4 turns per inch you set the lathe to thread pitch to match and wind the wire around a non conductive cylinder such as wood or plastic.


----------



## benmychree (May 8, 2018)

kd4gij said:


> The OP is talking about winding coils not gutting threads. To wind 1 1/4 turns per inch you set the lathe to thread pitch to match and wind the wire around a non conductive cylinder such as wood or plastic.


I stand corrected, he is talking about a LEAD of 3/4" (pitch between threads), but the issues with strain on the machine still exist.


----------



## kd4gij (May 8, 2018)

He is winding wire not cutting threads. The tension on the wire is the only strain witch isn't much.


----------



## benmychree (May 8, 2018)

The strain is not on the rotation, it is on the vastly speeded up gear train that drives the lead screw.


----------



## Bob Korves (May 8, 2018)

kd4gij said:


> He is winding wire not cutting threads. The tension on the wire is the only strain witch isn't much.


It is also trying to move the at rest carriage assembly, all in one big bump.  Inertia at rest must be overcome.  Can lead to a failure in the drive train.


----------



## wa5cab (May 9, 2018)

The Atlas gears and some other parts are NOT made of pot metal.  They are made of Zamak V which is a well known Zinc alloy.  Pot metal may contain Zinc but also typically contains a significant percentage of lead, contamination with which being thought to be one of the causes of Zinc Pest in Zamak.  Repeating the pot metal statement when aimed at a specific badge is considered deliberate badge bashing, and therefore an attempt to insult any member who owns the badge, neither of which are tolerated on this site, let alone this particular Forum.


----------



## wa5cab (May 9, 2018)

Gearhead (if you are still around), I believe that I have identified the Version of the MOLO that you are using as V8, because it appears to be the only one where the chart for cutting odd threads with a lathe equipped with a QCGB appears on page 133.  The A,B,C,D positions are in the case of A and B, somewhat arbitrary and once you have determined that one of the two 64T gears needs to be mounted in the top longest slot, you just need to mesh it with the 20T gear after you have meshed the other 64T gear with the gear in the gearbox (using a strip of typing paper to set the gear clearance).  After both nuts are tightened, raise the quadrant (AKA Banjo and Change Gear Bracket) with the strip of typing paper between the left 64T and the 32T half of the 32T/16T compound gear and tighten the clamp.  Then remove the paper.

Put the lathe into back gear and position the belts for 28 RPM.  With no left or right load/resistance applied to the carriage (which there won't be), the force needed to move the carriage will be approximately the same as it would be with the GB set to 15 TPI, the lathe in back gear, and the spindle RPM set to 345.  Carriage speed would be approximately the same.

Note that if you were actually cutting a thread, the situation would be a little different after the first several passes because the coarser thread is deeper.


----------



## derf (May 9, 2018)

You're winding wire......forget about the gearing and just eyeball it!


----------



## wa5cab (May 10, 2018)

Well, maybe.  But at that pitch it sounds like it might be for a tank coil for 10, 6 or 2 Meters which is a little more than just "winding wire".


----------



## T Bredehoft (May 10, 2018)

I wind springs often. I always wind them tight then stretch the finished coil as needed. No worries about so many turns per inch when winding. I do not use the leadscrew when doing this.


----------



## wa5cab (May 10, 2018)

Yes, but except in a couple of minor cases, the electrical behavior of a coil is unrelated to the mechanical behavior of a spring.  If the OP wants to make several interchangeable copies of a coil with an Atlas lathe, there is no practical reason why he can't, regardless of what the gears are made of.  The forces acting upon the gears driving the carriage will be the same while winding a coil as they are with the machine just running with no wire being wound.  This would of course not be true if the carriage was cutting a thread.


----------



## derf (May 10, 2018)

Think about this:  If the lathe has an 8 pitch lead screw, it has to turn twice as fast as the spindle to make a 4 pitch thread. For an 1-1/4 pitch, it has to turn 10 times as fast as the spindle. Something that little machine was never engineered to do.


----------



## T Bredehoft (May 10, 2018)

I, too, misunderstood. thinking of a coil as being just a coil of wire, not an electrical device. Being a tool maker I can't imagine an electrical coil with a spacing of perhaps 1/8 of it's length? or more, or less? A coil to make an induced magnet? or like an ignition coil to make a high voltage spark? 
Boy Houdy, how much I don't know!


----------



## wa5cab (May 12, 2018)

Tom,

I think that you are still not thinking of the proper type of coil.  Usage of coils with much more than one diameter spacing between turns is generally for one or both of two reasons.  One is that the inductance of a coil used from HF up through UHF is usually such that the total length of the wire in the coil would only be from a few tens of inches down to a few inches.  The other is that depending upon the power level and the altitude at which you are operating, you may have to space each turn at least several wire diameters apart just to prevent arcing between turns.  For example, the BC-610 plate tank coil for 18 MC is about 4 inches in diameter, made of plated copper tubing, and with a turns spacing of about an inch.  Only peripherally related to metal working.  But that's just the way things are done.

Derf,

You still aren't getting the picture.  To begin with, you can't reasonably call a 12x36 lathe a "little machine" unless you're just trying to be insulting.  If you spent your days running a 96x480 lathe (which I did - once) maybe.  But there aren't many of those around.  

If you were running the spindle at 2000 RPM, even a larger and much more expensive machine would beat its lead screw to death if it were geared to move the carriage forward 1-1/4" every time that the spindle made one revolution.  It would be turning at 20,000 RPM!  But as I also already said once, running the spindle at 28 rpm, the lead screw is only turning at 280 RPM which is only 4.667 RPS.  Well within the capability of all but the Atlas 618, and that only because its slowest spindle speed is 58 RPM.  The one precaution that I would take would be to see how long it takes the motor to spin down to a stop after I opened the motor switch, so that you have a feel for how much room you need.


----------

