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Cutting Metric Threads Through A Qcgb On A Craftsman 12x36

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mickri

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#1
Some of my projects will involve cutting metric threads and I wanted to figure out how to cut metric threads on my 12x36 lathe.
I know that there are numerous threads and videos about how to cut metric threads on an inch lathe all over the internet. I think that I have read most of them. There are mind numbing discussions about this gear or that gear and combinations thereof and error rates taken out 5 & 6 decimal places. But virtually all of the threads and youtube videos seem to assume that the reader already knows and understands how the gears work. Well for a newby like myself you are just stuck out in left field trying to figure this puzzle out. Especially how it works with a qcgb.
The first speck of light at the end of the tunnel came when I ran across a video on cutting metric threads through the qcgb on a South Bend model A 9 lathe.
What this guy did is gear his lathe so that his carriage moved 6mm instead of 1 inch in 8 revolutions of the spindle. I may be using some incorrect terminology here. To do this he geared his lathe so that the lead screw spun 1.89 times faster than normal using 54 & 80 gears instead of the normal 20 & 56 gears on his South Bend. With this change his lathe when set to cut 8 TPI now cut 6mm. 12 TPI cut 4mm, 16 TPI cut 3mm. 24 TPI cut 2mm, 32 TPI cut 1.5mm, 48 TPI cut 1mm, 64 TPI cut .75mm, 80 TPI cut .60mm, 96 TPI cut .50mm, 160 TPI cut .30mm and 192 TPI cut .25mm. I thought to myself why wouldn't this work on my 12x36.
I was now on a quest to figure out this intellectual challenge and was getting nowhere fast. Until I ran across a thread on this forum about slowing down the speed of the lead screw on a craftsman 12 with a qcgb. http://www.hobby-machinist.com/thre...on-a-qcg-late-model-12-craftsman-lathe.39019/ I want to give a huge thank you to Robert D for his explanation of how changing the gears effects the speed of the lead screw.
With this new found knowledge I set to trying different gearing until I found a combination of gears that would spin the lead screw approximately 1,89 times faster than normal. The closest that I have found so far is replacing the normal 40 gear with a combination 56/44 gear run off the inner 32 gear and replacing the normal 48 gear with a 40 gear. With this gearing the lead screw moves 5.988 mm in 8 revolutions of the spindle which is an error of only .002% if I got all of the math correct.
So am I totally lost here or did I figure this out correctly?
Chuck
 

wa5cab

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#2
I think that you are probably right but a member of the Yahoo Atlas_Craftsman group came up with a method for cutting at least some common metric thread pitches on an Atlas QCGB equipped lathe without affecting most of the Imperial pitches. It works on all 10" and 12" machines with QCGB. The expense consists of one 42T and one 54T gear, and giving up being able to cut 4.0 through 7.5 TPI without getting your hands greasy. All of the thread pitches from 8 TPI through 96 TPI are still available. I had intended to do up a formal threading chart for it but haven't had time.

You will find a detailed explanation of the method (with photos) in DOWNLOADS under Atlas/Craftsman/AA\A/C Lathes\A/C Lathe Charts, Tables, Metric & Misc Docs. File name is A30secondmetricconversion2rev2.PDF. It is currently at the top of the list in Downloads as I just uploaded it but of course it won't stay there as more files are uploaded.

Cutting metric threads isn't on my bucket list but I bought a pair of gears from Clausing JIC.
 

mickri

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#3
I had seen what must of been an earlier version with no pictures of what you uploaded. What I had seen only mentioned being able to cut the 1.00mm, 1.25mm & 1.50mm threads and I wanted to be able to cut some of the finer metric threads so I kept searching. After reading what you uploaded I will go that route. I will try to do the math to see what other metric threads can be cut and do a threading chart. It may take me a couple of days to get it done. I'll post the results. Now I have to decide do I try to make the gears or just buy them.
Thanks for you help.
Chuck
 

wa5cab

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#4
Right. Carvel originally posted this idea early this year. More recently, he (or maybe it was I) decided that the information should be expanded and placed in Files for downloading. He asked me to proof-read his edited copy and if I had any, make suggestions for changes or additions. It occurred to me while doing that that there were other metric threads that it might be close enough to cut, and I came up with a few of the more obvious.
 

Rob

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In addition to what Robert posted they also have a section in the MOLO on doing metric threads with a QCGB. I also have what I believe is out of an earlier MOLO that has a lot of other feed setups. Atlas10QCgearsetups.pdf Maybe Robert can tell me which one it came out of as I would like to find it in a printed copy.

Also when doing metric threads you need to be careful when releasing the half nuts. Some places say to never release them until the thread cutting is complete. Another site I read and what I did was when you release them you turn off the lathe at the same time. You then pull out of the work, next you reverse the lathe and when the thread dial is at the place you released from you engage the half nuts and let the carriage move past the end of your threads. You then turn off the lathe and place the motor in forward, set the cross feed for the next cut and do the process again until completed. I did this to cut metric threads on a ER 32 collet chuck I made.

IMG_1571.JPG IMG_1574.JPG
 

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#6
Rob,

Your PDF is a copy out of a version of the MOLO (because the right half of the last page shows the tab divider for 8 - LATHE ATTACHMENTS) that I didn't know existed. Because the page numbers start with "1" instead of around "95", it is from one of the versions that all say COPYRIGHT 1937 on the copyright page on the back side of the title page. Because it covers the Atlas 1500/1700 the MOLO was printed between 1947 and 1952, the years that those models were in production. There may be a few of them around but I routinely ask eBay sellers which lathe make, model and size is mentioned on the first page of Part 7 - THREADING, and so far haven't turned up anything except either the Atlas F-Series 10 inch or the Master Craftsman 12 inch. But I accidentally bought one about a year ago (think it was something else) that turned out to cover the Atlas 6 inch so have been looking for one covering the Craftsman 6 inch. I'll add Atlas QCGB to the list.

The exact pages that you have a PDF of were also printed as a standalone and sold with the QCGB conversion kits. My friend in South Africa has the only original I know of. But one could turn up one day. He scanned it and sent it to me. I converted it to TIF and did some cleanup. And you can have a PDF copy of that if you wish. It's in DOWNLOADS in the Atlas Lathe Manuals category, I think. If I didn't upload it, let me know.

One last comment before I quit for dinner. If you look on page 4 (printed page #, not file page #) of your PDF, you will see that you could have cut the metric threads (nice job, BTW) with less trouble if your machine has a FWD-OFF-REV switch. For the ID threads, the process is the same except that instead of backing the cutter "Out" after each pass, you back it "In".
 

mickri

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#7
Rob,
Thanks for the input. One of my projects is to make an ER chuck which requires metric threads. Hence my research into metric threading. I saw the info on metric threading in the MOLO and it seemed like you had to change gears for every thread. That is probably more precise but over the short, 1 inch or less thread lengths that I anticipate I think that I will be fine with the settings posted above. Had some time this afternoon and did a metric thread chart. I did the math for every TPI on the qcgb. Most of the threads were not usable so I did not include them in the chart I made. My chart is a simple excel spreadsheet. A copy is attached.
 

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#8
Thanks. That saves me some time.
 

Rob

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Robert, Thanks, I was able to find the PDF of the QCGB and it is a lot nicer copy than the one I had. I think I will print that one out as I like to have a printed copy by the lathe.

Also I do have a reverse switch but when you are threading to a shoulder you need to be able to release the half nuts. You just need to make sure that the threading dial does not do a full turn but that is not a problem. My explanation might not have been so good.
 

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Rob,

I don't understand why you have to release the half nuts just because you are threading to a shoulder. Cut a thread relief to give you a little lee-way. And use a much lower spindle speed or surface speed than you would use for turning the same material. And don't run your belts loose.
 

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#11
Problem with that setup (and with the table in all of the later MOLO's) is that if you acquire a lathe equipped with QCGB (either new or used), it only comes with three change gears (40T and two 48T). So standard set or not, you still have to buy a bunch of gears.
 

mickri

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#12
I was going back over my original calculations and did more research on how gears on a lathe work to see if I could keep the inch TPI from 8 up and still convert the 8 TPI setting on the qcgb to 6mm like Carvel had done with converting the 60 TPI to 1mm. In doing this I discovered that I had made an error in my calculations. The correct combo gear is a 51/54, not a 44/56. With the 51/54 combo gear and the normal 40 idler on the inside you have the 32 driving the 40 idler which drives the 51 and the 54 drives the 32 gear on the Qcgb to cut metric threads. With the 40 idler on the outside driving the 54, now an idler, driving the 32 on the Qcgb you can cut all of the inch threads from 8 TPI and up.
I thought that it was best to correct the error in my original calculations. I hope that I got it right this time.
Chuck
 

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#13
Rob,

Your PDF is a copy out of a version of the MOLO (because the right half of the last page shows the tab divider for 8 - LATHE ATTACHMENTS) that I didn't know existed. Because the page numbers start with "1" instead of around "95", it is from one of the versions that all say COPYRIGHT 1937 on the copyright page on the back side of the title page. Because it covers the Atlas 1500/1700 the MOLO was printed between 1947 and 1952, the years that those models were in production. There may be a few of them around but I routinely ask eBay sellers which lathe make, model and size is mentioned on the first page of Part 7 - THREADING, and so far haven't turned up anything except either the Atlas F-Series 10 inch or the Master Craftsman 12 inch. But I accidentally bought one about a year ago (think it was something else) that turned out to cover the Atlas 6 inch so have been looking for one covering the Craftsman 6 inch. I'll add Atlas QCGB to the list.

The exact pages that you have a PDF of were also printed as a standalone and sold with the QCGB conversion kits. My friend in South Africa has the only original I know of. But one could turn up one day. He scanned it and sent it to me. I converted it to TIF and did some cleanup. And you can have a PDF copy of that if you wish. It's in DOWNLOADS in the Atlas Lathe Manuals category, I think. If I didn't upload it, let me know.

One last comment before I quit for dinner. If you look on page 4 (printed page #, not file page #) of your PDF, you will see that you could have cut the metric threads (nice job, BTW) with less trouble if your machine has a FWD-OFF-REV switch. For the ID threads, the process is the same except that instead of backing the cutter "Out" after each pass, you back it "In".
Hi John UK here.I am fortunate in having two copies of MOLO,both different.The older one has a black cover and the circular Atlas logo at bottom rightl says "Atlas Quality Shop Equipment since 1919" and is Metal ring bound.It has the section 7 threading Tab but no pages.and It gas no copyrite or printing date .
The other has a grey front cover and plastic ring binding. the reprint information rages from 1938 to 1960.It also has the threading suppliment.
I am assuming the Black wire bound version must be a very early publication with having no print or reprint dates inside.
What do you guys think.?
 

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#14
The gray cover one is a 1960 Eighteenth Edition. It covers the early version of the 1/2" bed machines. From 1954 on, there were black cover (Craftsman) and gray cover (Atlas) but the contents as far as I have found are the same each year. And both cover colors have the same Edition number. From 1937 through 1952 there were no Edition numbers and no list of Reprint years. During those years, there were at least seven and possibly eight different versions printed, plus some minor changes. But I have never seen one from that period that on the back side of the Title Page did not say Copyright 1937. In the front of the book, the first page should be blank front and back. Then should be the title page and on the back the copyright page.

The actual First Edition was exact bound (glue and staples). The cover printing is slightly different from the later 1937 black cover ones. I do not know whether it was printed one year or two because only one of the apparently 1937 catalogs has a photo of it. Then for a few years there is no photo. I don't know what color the first cover was as the catalog is gray scale and I have never found an example. Some time after 1937 (could have been as early as 1938, the cover color was blue and they were spiral (metal wire) bound. I have two of those and they cover the original 10 and the 10D. Then covers changed to black (all with the Atlas logo), nothing was bound in behind the 7-Threading tab, and they were supplied with a loose supplement covering either the Atlas 10F or the Sears Master Craftsman 12". The 12" supplement would apply to the 101.07362 through the 101.07403 (no 96T gears). Those were, AFAIK, all wire bound although some were full length wire, some had two separate segments of wire. And some had three. Your black cover one is probably one of those. Assuming that there was only one printing each year of each type, best guess is 1939.
 

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#15
Some of my projects will involve cutting metric threads and I wanted to figure out how to cut metric threads on my 12x36 lathe.
I know that there are numerous threads and videos about how to cut metric threads on an inch lathe all over the internet. I think that I have read most of them. There are mind numbing discussions about this gear or that gear and combinations thereof and error rates taken out 5 & 6 decimal places. But virtually all of the threads and youtube videos seem to assume that the reader already knows and understands how the gears work. Well for a newby like myself you are just stuck out in left field trying to figure this puzzle out. Especially how it works with a qcgb.
The first speck of light at the end of the tunnel came when I ran across a video on cutting metric threads through the qcgb on a South Bend model A 9 lathe.
What this guy did is gear his lathe so that his carriage moved 6mm instead of 1 inch in 8 revolutions of the spindle. I may be using some incorrect terminology here. To do this he geared his lathe so that the lead screw spun 1.89 times faster than normal using 54 & 80 gears instead of the normal 20 & 56 gears on his South Bend. With this change his lathe when set to cut 8 TPI now cut 6mm. 12 TPI cut 4mm, 16 TPI cut 3mm. 24 TPI cut 2mm, 32 TPI cut 1.5mm, 48 TPI cut 1mm, 64 TPI cut .75mm, 80 TPI cut .60mm, 96 TPI cut .50mm, 160 TPI cut .30mm and 192 TPI cut .25mm. I thought to myself why wouldn't this work on my 12x36.
I was now on a quest to figure out this intellectual challenge and was getting nowhere fast. Until I ran across a thread on this forum about slowing down the speed of the lead screw on a craftsman 12 with a qcgb. http://www.hobby-machinist.com/thre...on-a-qcg-late-model-12-craftsman-lathe.39019/ I want to give a huge thank you to Robert D for his explanation of how changing the gears effects the speed of the lead screw.
With this new found knowledge I set to trying different gearing until I found a combination of gears that would spin the lead screw approximately 1,89 times faster than normal. The closest that I have found so far is replacing the normal 40 gear with a combination 56/44 gear run off the inner 32 gear and replacing the normal 48 gear with a 40 gear. With this gearing the lead screw moves 5.988 mm in 8 revolutions of the spindle which is an error of only .002% if I got all of the math correct.
So am I totally lost here or did I figure this out correctly?
Chuck
Even though I have the gears for metric threading setup I found a simple work around for short Metric threads.
A close approximation on standard QCGB for 1 mm pitch is 26 tpi.for 0.75 is 32 tpi and 0.5 is 50 tpi.
If the threads you are cutting are only short this may work for you and you can allways run a metric hand chaser over just to clean up
the threads.It works for me.
 
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mickri

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#16
I finally got the gears that I need to be able to cut metric threads through the qcgb. Went to replace the two 48 gears with the 44 & 52 today and discovered that the two 48 gears are a combo that are attached together. My parts manual showed them as individual gears on a stud. Also discovered that the 40 gear is fixed to its shaft. Not that big of a deal. I found some stud assemblies on Ebay at a cost of $25 plus $7 shipping. Is that a fair price? The Ebay listing has a best offer option and I would like to make a lower offer but still want to be reasonable.

Besides the metric threads that I can cut with the 44/52 through the qcgb I will need to cut a 1.8mm thread for a future project. This thread requires different gears. The gears are the 16 driving a 48 idler which drives a 54 on a 54/44 combination with the 44 driving a 32 idler into the qcgb. I had planned on using one of the 48's but can't do that now. I don't really want to buy a 48 gear that I will probably never use again after this future project. If the 40 or 52 that I have will work clearance wise any reason why I can't use one of these in place of the 48? I will also need several spacers. I don't have any and have not been able to find any for sale. I will have to make them. I am sure that the oem spacers are made of steel which might be hard to cut the internal keyways. Any harm in making the spacers out of aluminum, brass or even plastic? I could even make one by molding thickened epoxy around the stud. I have a lot of experience working with epoxy.
 

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#17
You could try Clausing for the Spacers and the stud assemblies. They still support most of the parts for our lathes. The new splined assy to combine the gears are a hard plastic. I have a couple and they seem to work just fine. I believe that I paid about $10.00 for them. I had a 40T gear that was seized to the splined assy. I was able to chuck up the gear and bore out the center and I was able to save the gear.
 

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#18
Mickri,

You are the first person to ever mention finding either the strange dual 48T or the 40T stuck on its bushing. The 40T is the so-called Sliding Gear that you reposition to cut the coarsest threads (like 4 TPI). So it definitely is not supposed to be stuck to the keyed bushing. And I suspect that the two 48T's have the same problem. You need to make proper drivers and receivers and use an arbor press (NOT a hammer) to get the bushings out of them. Most likely, a PO didn't keep the machine properly lubricated.

If, as you say, all of the gears will mesh up, no. The 48T as described is just an idler. Idler gears do not change the over-all ratio regardless of where they are or what their tooth count is. They are generally picked from what's available (meaning that they don't need to be used anywhere else) and are of a size to help make the other gears fit up conveniently.

I would see nothing wrong with making a spacer out of aluminum or brass. Maybe not plastic, though. The only problem will be broaching the double keyways exactly 180 deg. apart. You can also use any gear that you have that will install without its teeth touching the teeth of another gear.

At least a few months ago, Clausing still had them in stock. If you have any gears with bad teeth, you can also modify them. Or you might be able to use another available gear as a spacer. The only requirement is that they don't touch any other gear.

About 16 months ago the factory prices on the bushings and studs were as follows:

9-70A $9.32
9-73A $22.56
9-69A $? (I didn't order any)

So $25 sounds reasonable. $7.00 for shipping is OK if shipped PriMail, high if shipped First Class Mail, and dirt cheap if shipped either UPS or FedEx Ground.
 

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#19
Rob,
Thanks for the lead on parts. I will get in touch with them.
 

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#20
Hi Robert,
The two 48's are definitely not stuck on a bushing. There is no key way that I can see and the bushing holding the gears together is slightly rounded over on each end. As for the 40 it could be stuck on a bushing but I don't think so. It is on a bushing but there is no spacer to keep it in place. Something is holding it in place to keep it from sliding on the bushing. I'll look at closer tomorrow.
 

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#21
Robert,
After your comment about me being the first to ever report a dual 48 gear I had to go out into the garage and take a closer look. Sprayed some PB Blaster on the 48's and the 40. What I thought were the rounded over ends of a bushing turned out to be a washer that was stuck to the gear from old, dried grease. The PB Blaster dissolved the grease and the washer fell off into my hand. A couple of lite taps with the handle of a screwdriver freed everything up on both the 48's and the 40.

I am still curious about not having a spacer on the 40 sliding gear to keep it in place.
 

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#22
Installed the gears today. I can now cut the common metric threads while still retaining the imperial threads from 8 tpi up. I also have realized that no spacer is needed on the 40 sliding gear because the thin washer on the combo gear keeps the 40 in place. I was surprised at how tight the bushing fits into the gears.

IMG_3598.JPG
 

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#23
mickri,

If you will read the operating instructions on the QCGB, you will see why the 40T gear is called the "Sliding Gear". You've already figured out why there is no need for a spacer. If you did the conversion following the instructions in "A 30 second metric conversion Version 2 Rev2", you'll already know that installing the 52/44 tooth gear pair only cost you the ability to cut 4.0 to 7.5 TPI threads. You use the sliding gear to switch between Imperial and Metric. You should go to Downloads also and get QCGB MM-Inch Thread Charts Atlas And Craftsman.pdf.
 

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#24
I downloaded all of the documents you mentioned and more months ago. One document that I have downloaded and may be one of the ones you mentioned has every possible tpi that can be cut through a qcgb by changing the gears. It was from that document that I found the gears that I would need to cut a 1.80mm thread. I converted 1.80mm to tpi which is 14.11 tpi and scanned the document to see if any combination of gears would cut 14.11 tpi through a qcgb. I found a listing for gears to cut 14.1136 tpi and those are the gears that I referenced in a prior post. I know that with the change I can no longer cut threads from 4 to 7.5 tpi and that all threads from 8 tpi and up can still be cut.
 

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#25
OK. Sounds like you mostly have the situation under control. But one of the two files that I mentioned was not uploaded until this afternoon.
 

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#26
Using the 51/54 or 63/60 gear combinations are only an approximation, the correct gears are 127/120 this will give a true metric pitch, the problem is that a 127 t gear is quite large and will not fit on many smaller lathes, but should fit on most 12" and even some 10" lathes.
 
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