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zabelo
08-20-2004, 09:57 PM
Somebody PLEASE explain to me how to thread on one of these small lathes.
I am a Machinist by trade but I will admit
most of my time as a machinist has been spent
on big boring mills and verticle lathes.
I do thread on a tool room lathe from time to time and have no problems but I just can't
figure out cutting threads on this Birmingham.
It is a 11" x 26" with one screw for both feeding & threading.The thread chart looks like this.

LEVER I II I I I II
a| 45 48 36 36 36 36
b| 40 40 40 44 46 40
B| 8 9 10 11 11.5 12
A| 16 18 20 22 23 24
C| 32 36 40 44 46 48

It has 2 levers one marked A B C and an other
marked I II III.

Any help would be great!!
Maybe a website or a book?

wierdscience
08-20-2004, 11:17 PM
There apear to be lots of repeats in that selection,also upper and lower case letters,that might indicate a set of stud gears that need to be reversed to achieve the different pitches.

Other than that a 16 pitch looks as simple as lever one in "A"position and lever two in "I".Did you try this and have problems?

zabelo
08-20-2004, 11:50 PM
Thanks wierdscience,
Yes there is a lot of repeats and thats only half the chart.
I tried every combo and never got a feed that was even close to threading speed. I must be missing something simple.I have never turned on this type of small lathe before I bought this one.Every project I work on I need to cut threads and it is bugging the hell out of me.Birmingham and their distributor were no help.

any other thoughts?
thanks,
Zabelo

gizmo2
08-20-2004, 11:55 PM
This is a stab in the dark, as I've nevr had a Birmingham. But I did have a 9x20 Jet for a time, and somewhere on there should be a plate telling you which is shaft 'a' and 'b', and those will get the change gear with the tooth count indicated.
The Jet just had a two position lever, and from your chart it looks like yours might just use two of the three for threading. As Wierd suggests, try a 45 tooth on one stud, a 40 on the other, lever I, tumbler A and see if it gnaws out a 16tpi. Look for the location marker inside the gear cover if it ain't up front, and best of luck.

Don Young
08-21-2004, 12:01 AM
The lower case letters do not make sense to me as they indicate that the feed does not change when the other lever is moved through several different positions.
One possibility for your problem might be that you are engaging the feed clutch rather than the threading half nuts, assuming that your lathe has both.
Hope this helps.

Al Messer
08-21-2004, 07:37 AM
Who makes it?

suprdvn
08-21-2004, 08:51 AM
It looks like you won't be cutting 1/2-13 threads anytime soon. http://bbs.homeshopmachinist.net//frown.gif

nheng
08-21-2004, 09:24 AM
Does it look like this Grizzly G9972Z ? It's got I, II, III, A,B,C.

http://www.grizzly.com/catalog/2004/415.cfm?&gid=DFF26CE1-5BBE-4AE7-837D-369382D26409&site=grizzly

They don't have a link to the manual for this one but maybe they would email it to you.

zabelo
08-21-2004, 02:08 PM
Thanks everone for all your input.I finally got it.There is no feed clutch just a half nut.It's sold as a Birmingham but looks like it's manufactured by the same co. as Grizzly.I was told I didn't have to change any gears for standard thread but I do.There is six different gear combos plus one for feed.WOW!
The lower case a and b are the different gears, upper case A B C are for one lever and I II for the other.The face plate was damanged from shipping and a chart showing wich stud was a and b was missing but I now know wich is wich.
I realy wish I had researched lathes before I purchased this one.I would have bought a SB 9x20.Maybe I'm just a spoiled CNC man but changing all these gears for threading(which is about four steps)and belts for speeds and gears again for feeding.Holy Moly!
Thanks again for all your help.
Zabelo

docsteve66
08-21-2004, 02:40 PM
Edit comment: the below was started right after weird,s comment- way back when it might have been of use. Read no further.
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I suspect the weird one, as usual on sniffing on the right trail. You probably have a set of wrong gears from the spindle to the ABC lever. Forget about threading, looks to me as though your problem is really that you can not find the feed rate you want- you want a feed rate that corresponds to screw thread sizes and are getting something else, but the rate you get IS repeatable is it not? If it ain't repeatable then you have slippage- a clutch, shear pin, some lost motion. If the problem is lost motion- read no farther.

To get down to basics, and I may be missing something important. From the info you give, Your ABC lever is probably a 1:1, 2:1, 4:1 link/ratio between the lead screw and the gear train. Easy one to check- count the TPI of your lead screw and turn the gear mounted on the input to your ABC lever. Lets assume your lead screw is 8 TPI. 8 turns of the input gear should move the carriage exactly on inch for turns or 18 or 32 turn of the gear. I am guessing you have an 8 TPI lead screw only because of the figures you gave being so easily divided by 8. Any way, checking the ABC lever is easy. I bet you find it is OK.

That only leaves the numbered lever to figure out. I think I would go to machinery hand book or find that free program for calculating feeds based on numbers of gears and teeth, count gear teeth on spindle and the gears in the power train, disregarding any "idler"gears. Some simple work with fractions and You will have a figure that gives the fraction of an inch one spindle turn should give. Bet you a beer, the feed is as you calculate. If that is true,then you are doing everything right and need to juggle the gears you have or get another gear or two or more.

Keep in mind that, on an older machine (especially one for sale) that the last owner may not have been able to cut standard threads either, that the thread cutting gears may have worn out, maybe the previous owner wanted a "fine finish" and re-arranged the gears to give the slowest possible feed. Sometimes all a repairman has to cling to is "this thing used to do XXXX, I can make it do that again". Too often you discover the machine could not have done what you believed or were told it did do. In your case, you do not know what the machine could do immediately before you got it. I am reminded of the kid who told me his oil burning four banger could do 100 MPH in 15 seconds before "Joe " changed his sparking plugs and he would like to use my plug cleaner. but I digress.

Might be we could "howlp" you if you posted the gears available and lead screw pitch. Be sure you keep track of the driving and driven gears if you use the hand book formula. Dial indicator to measure carriage travel is nice but needed- just use a rule to get the pitch and mark the ways after twisting the lead screw (after taking out the back lash).
Steve


[This message has been edited by docsteve66 (edited 08-21-2004).]