Delta Rockwell 11" change gears

C

chucksue

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I bought this lathe about 30 years ago. I have made lots of parts on this lathe. The problem is I can't cut threads on it. The gear arrangement is the same as in the photo posted by Thenrie. There is no number on the lathe. Where the two gears off the quick change for the feed rate of the tool is with two 48 teeth mine has one 40 tooth gear. I set up a dial indicator on the carriage and set the lathe for a 13 threads per inch cut.
I engaged the threading lever (with the motor not running) and turned the head one revolution by hand. My travel was .050 and it should be .07692.
The 24 tooth gear is on the shaft. I have the manual that came with the lathe. Am I right in assuming the 40 tooth gear is wrong and I need two 48 tooth gears to make it travel at the right rate to thread?
 
Measuring the advance of the carriage for one revolution with a dial indicator can be difficult, but if you divide 1 by .050 you get 20... , so perhaps you are currently set for 20 TPI. It will be more accurate to measure, say, 10 revolutions and divide by 10.
 
Yes by using ten it cuts down the error. I have put a 1/2 rod with 13 threads and watched the cutter track the thread . That is how I found out the feed was wrong. I know the selectors for 13 threads are set right. Thank you for your reply.
 
Does the gear train start at the spindle, with all gearing visible to the QC box? Does it have a QC box?
 
It has a quick change box. On Ebay there is a lathe posted like mine. www//ebay152118758114 . Gear train starts at the spindle. Has the reversing two gears to change the travel from left to right and right to left. They go thru a 60 tooth to a 24 tooth and then down to the QC which should have a 48 tooth gear. here is where mine has a 40 tooth gear. If you type in delta rockwell gear train and look at the images the gear train is shown. I don't know how to post the address.
 
The reason I asked about the gear train is that it is all basic math. You have a lead screw with a certain pitch. Let's say it is 8 tpi, threads per inch. If you had gearing that overall made the ratio of spindle to lead screw one to one, then you would be making an 8 tpi thread. If you changed the gear on the shaft that drives the QCGB to one with twice as many teeth, then you would be cutting 16 tpi. The gears in the QCGB further change the gearing. Interestingly, the gears between the spindle and the QCGB shaft, excluding the spindle and QCGB shaft gears, all add up to zero unless there is a gear offset in the train where two gears are connected back to back and you are using one gear as the driving gear and another for the driven gear, then they count in the train. Otherwise, it does not matter if you have 12 or 100 teeth on a gear between the spindle gear and the QCGB shaft gear, the ratio will not change there. Is the QCGB missing the threading chart? If it is there, how about posting a picture of it? If not, we will need to know the model of the lathe to possibly be able to help you.
 
The QC chart is there.It is in great shape. The tag for the model is gone. I think it is a 25-100. I found that by just searching the net. I used the formula ( gear # teeth plus two divided by the diameter of the gear ) and found that all the gears have a DP of 16.
I will try to take some pictures and post them.
 
That is where I found out the feed rate was not 13 threads per inch. I think that is where the 40 tooth gear on the QC shaft is messing me up.
 
The chart should show the gears required and the tumbler positions for the various threads. As Captain Piccard would say, "Make it so."
 
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