1940-41 sb 8113c reverser gearing
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  1. #1
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    Default 1940-41 sb 8113c reverser gearing

    img_20190830_123520.jpgimg_20190830_123433.jpgimg_20190830_123449.jpgI bought this lathe several years ago and have done a fair bit of turning and some threading on it. At purchase the reversing tumbler mechanism was a botched up thing consisting of a brass bushing screwed to a thick plate with a slot to shift position. The bush was turned to fit into the headstock and the center was bored to carry the shaft for the stud gear. Much of this is not concentric, and there is wear in the id. The pair of tumbler gears do not have the same number of teeth. Although there seems to be a spare 24 tooth gear which could be used to make a matched pair. There is also a spare spindle gear of 33 teeth. I think some the gears are original, while others appear to be to thin. I believe some of the change occurred when the original cast reverser was destroyed (?) other changes are perhaps an attempt to cut metric threads.
    the spindle is clearance for 1 inch
    the lead screw is 6 tpi I believe
    it is a single tumbler qc box
    I would like to tidy all this up and return it to near as possible original.

    Can any one help me with the following Questions:

    1) should the tumbler gears be a pair of 24 tooth gears?
    2) what tooth gears should be the inner and outer gears on the on the stud shaft be?
    3) if the cast reverser plate is interchangeable with any other size sb lathe. 13s appear to be uncommon
    4) is there a current good source for gears

  2. #2
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    If you are threading with it and the threads are exactly what you selected with the QCGB all the gears are correct in tooth count. The reverse gears are only for that: reverse rotation. They are only an idler gear. Generally gears in a gear train are the same width but not always. So to answer your first question. It doesn't matter as along as they mesh properly. Two gears of the same size may not work in your case. Second question: Here is where tooth count will make a difference. The outer stud gear in some cases can be changed to increase the number of threads that can be cut with the QCGB. Third: Not too many lathes interchange with one another. Fourth: Many members here have gears that can help you but we need the tooth count, DP and PA. Sometimes pitch of the gears can change at the stud gear combo if someone chose to do that. Sometimes if it is working fine leave it alone and use it.

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    Check with Ted. ( latheman2 with the typical aol domain address ) If he does not have replacement OEM gears ( NOS or even gently used ) he will know who might. They are supposed to be 27T Twin Gears on a 13". We make replacements for them and have them in stock, but they are an upgrade type of replacement and slightly more expensive. If Ted does not have them or know where you might find them, there are several members here that might have some laying about. Some, simply from purchasing new ones from us, leaving their old ones orphaned on a shelf. Good luck.

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    thank you for the replies but I am still after a bit more information. The threads I have had to cut are square threads used in the drilling industry and while by changing the outer stud gear and thinning the thread I have managed to get a fit, just the use of the QC box has never matched perfectly.
    as mentioned in the first post the " twin gears" are currently not exactly the same in tooth number or in the way the gear fits its shaft. There is, however, an exact match to the larger (24 tooth gear) with the lathe. This leads me to believe that the original "twin gears" were in fact a pair of 24 tooth gears. In most set ups it is the most forward of the two twin gears that is driving the inner stud gear, but in the made up plate on my lathe it is the opposite. (see pic above) The inner stud gear is a 32 tooth gear. While this seems logical (same number of teeth as the spindle gear) it is much thinner than other gears in the tumbler system and with additional width welded to the boss. (I suspect it is not an original and may be the wrong tooth count) The 32 tooth inner stud gear does not seem to allow the fitting of two 24 tooth twin gears. This has all been brought to a head by the excessive play in the screwed brass bush in which the stud gear spindle runs. Because it is threaded to the plate there is no meat left to re bush the end nearest the inner gear. This , and the fact that the brass bush is not bored concentric to its outer diameter all adds up to poor mesh, noisy running and excessive wear. I am faced with having to replace the brass piece which slides into the head stock, possibly with a steel tube to which replaceable bushes can be fitted, or try or find an original cast reverser plate. Given that nothing was concentric in the first place if I reuse the steel plate the holes for the "twin gears" will have to be relocated to correct the mesh and the hole where the brass tube was fitted will have to be bored to accept the steel tube. Given the work involved I am very interested in getting it back as close to original specs as possible. It would be very helpful to know what the factory inner and outer stud shaft gears were, and what the original "twin gears" were. I have looked carefully at the rest of the gear train down to the QC box and am convinced it is unchanged from original, and is in quite good condition.

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    The “twin” gears are not twins in this case
    Attached Thumbnails Attached Thumbnails f0536cfe-fa36-44b2-832d-2c75fddca6f3.jpg  

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    Wow. So, does it take after the 16”, in this case? ( in similarity, not same ) Here I was under the impression that all 13” ones were the same. Silly me. What year did they change? Thanks.

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    Quote Originally Posted by Zahnrad Kopf View Post
    Wow. So, does it take after the 16”, in this case? ( in similarity, not same ) Here I was under the impression that all 13” ones were the same. Silly me. What year did they change? Thanks.
    This is a reverse bracket assembly for a 13” with the small spindle only.

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    Fact: The thin gear compounded with the stud gear you have should have the same tooth count as the spindle. The reverser gears can be any count as long as they mesh correctly. They are essentially idlers. They will change direction but will have nothing to do with the ratio between the spindle and the compound stud gear. They don't have to be the same count either. The pivot will determine the size of each gear. One has to disengage for the other to work properly. Those single tumbler gear boxes have an in/out along with the lever and tumbler selector. A quick check for you is to count the TPI on the lead screw. It is either 6 TPI or 8 TPI. Depending on which one it is line up your QCGB to the same thread that your lead screw is. Put a mark on the spindle and lead screw that you can watch. Turn the spindle one full turn. If the lead screw turns one full turn also then all gears are correct. If not you have a problem. Some one on here must have a SB like yours that can verify the gear train from the spindle to the QCGB. As for your thread cutting problems changing the gears will change the pitch not the profile of the thread.

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    While I was well aware of the nature of idler gears in the reverser, I would like to thank "tommy1010 "for a couple of useful nuggets. It is especially useful to Know that the inner stud gear should be the same tooth count as the spindle gear. I did suspect it was logical for there to be no net ratio change from spindle to stud gear shaft, even though it looks like that inner gear should be wider. the tip that selecting the same tpi as the lead screw to yield a 1 to 1 ratio between the chuck an lead screw should have been obvious, but I missed it. Every thing seems to match up when an 18 tooth gear is mounted on the outside of the stud shaft. The his is the smallest gear that can be used to engage with the rest of the gear train. I do have a few other gears that I have used in this position. I now have to concede that the set of 24 tooth tumbler gears wont be able to be used even though they look like the were made as a spare part. ( I will post some pictures when I next get to the shed) I will start modifying the bush on the made up reverser to take out the play while continuing to look for a whole unit second hand. It would still be useful if any one knows what the tooth count for the pair of tumbler gears is. Photos of a similar lathe would also be helpful. My lathe is a 8113c, small spindle (will take 1 inch through)manufacture date 1940 -1941, serial #105361. single tumbler QC box

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    Question

    Quote Originally Posted by john herrick View Post
    It would still be useful if any one knows what the tooth count for the pair of tumbler gears is. Photos of a similar lathe would also be helpful. My lathe is a 8113c, small spindle (will take 1 inch through)manufacture date 1940 -1941, serial #105361. single tumbler QC box
    Did you see post #5. ???


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