Oddball threads to lock the customer into buying parts only from the OEM was a widespread and common practice in the past. In fact, machinery builders would not only use non standard pitch for the diameter, but they would also select a pitch that wasn't among the standard set of pitches available on normal engine lathes. So, even though the customer may have an on site maintenance machine shop, he still wouldnt be able to duplicate the thread. Popular ones I've seen in the past when making repair parts for old machinery are 17, 21, and 23 tpi, none of which will be found on a standard lathe. Fortunately, the wide use of cnc machining now makes such tricks ineffective. If you want to duplicate a 17.6 tpi thread, for example, you just program the pitch into a CNC lathe and chase the thread just as easily as cutting a 1/2-13. For parts not adaptable to lathe work, the same process is used on a CNC mill where any diameter and pitch, both internal and external, can be produced via use of a thread milling cutter.
Hi folks. First post but I've spent many hours reading the great information on the site as well as watching and learning from Uwe's fine videos. For a bit of background, I've watched CL and the other usual local sites for a couple years looking for a compound walking foot machine at a reasonable price. Has about given up, but recently found a Consew 225 in like new condition for a good price. Bought it and added a Reliable servo motor, and I'm well satisfied with the total investment of about $500. The previous owner bought the machine in 89 when it was 5 years old from a local community college that discontinued an evening upholstery course due to lack of participation. He said he managed to make a seat cover for his truck, but decided sewing definitely wasn't his thing, so the machine sat for the last 30 yrs. He mentioned while I looked at the machine that he thought the thread tension assembly might need some attention as he recalled it seemed too touchy and difficult to get to a happy medium. I found the same, as in the tension on #92 bonded polyester will go from totally loose to locked up tight in less than a quarter turn of the knob. I've read some posts from other seemingly knowledgeable people on another site that the tension knob will be approximately flush with the end of the stud when the tension is in the normal range, assuming the tension assembly is OE and not aftermarket. Mine is OE, as the parts are stamped Seiko. But the stud protrudes about a quarter inch past the knob before the discs begin to tighten on the thread. Then, another 1/4 turn and it's dead tight on the thread. I'm thinking the spring may have been compressed beyond its normal limits by students who didn't know better. As a mechanical engineer by education and a machine shop owner by trade, I learned years ago that if you give the uninitiated an adjustment they can twist on conveniently, they're sure to twist until something bottoms out or breaks. So, my question is... Does this narrow range of adjustment sound normal? Or is it likely that the spring has been distorted and needs to be replaced? If replacement is in order, any suggestions for sources of high quality parts would be helpful. Thanks in advance for your help. Cliff