AlanT Posted January 28, 2015 Report Share Posted January 28, 2015 (edited) Some time back Motorsport Mickey asked if I would make some non-standard studs for the trailing arms. There have 3/8 UNC and 5/16UNF mixed threading and modified lengths. Here I am cutting the 3/8in threads. The length may look wrong but there is a reason for this. https://flic.kr/p/qFKi5X This is an Alfred Herbert CH die-head as would have almost certainly used in original production. This one was made in 1942 but is in perfect condition. The chaser-dies are NOS. It's interesting to compare the hardness of tooling from this period. Stuff made now seems like cheese in comparison to the diamond-hard surfaces on these. At this time Herbert was the largest machine tool firm in the world and funded the re-building of Coventry Cathedral. I worked with them in 1970 to convert some of their machines to CNC control. Unfortunately it was too late. The Japanese got well ahead with this being heavily funded by their government to make sure this happened. Edited January 28, 2015 by AlanT Quote Link to post Share on other sites
stillp Posted January 28, 2015 Report Share Posted January 28, 2015 Nicely done Alan. I've never used a proper diehead - what stops the thread from starting in a different place each time? Quote Link to post Share on other sites
AlanT Posted January 28, 2015 Author Report Share Posted January 28, 2015 There is a short run in on the die-chasers. But remember that the head is NOT driven. Its just sliding and is pulled along by the thread its cutting. I have it in the tailstock which is free to move. But I have a travelling-steady locked on the bed and eventually this stops the tail-stock sliding. Then the spring release in the head snaps it open. These maintain excellent consistency of cut length. Quote Link to post Share on other sites
peejay4A Posted January 28, 2015 Report Share Posted January 28, 2015 Nice job Alan. How do you hold it to form the thread on the other end of the stud? Quote Link to post Share on other sites
AlanT Posted January 28, 2015 Author Report Share Posted January 28, 2015 Holding them in ER25 collets. This is why I made the 3/8 thread too long. If the collet marks up the thread tops, I'll be cutting that bit off. Maybe the collet won't mark the tops and next time I can save a bit of waste. Depends on how tight I need to squeeze 'em. These chasers cut 15thou deep on each pass. If you were cutting these with a single point tool you would cut 5 thou. So you have to hold the feedstock pretty tight. Quote Link to post Share on other sites
stillp Posted January 29, 2015 Report Share Posted January 29, 2015 (edited) Holding them in ER25 collets. This is why I made the 3/8 thread too long. If the collet marks up the thread tops, I'll be cutting that bit off. Maybe the collet won't mark the tops and next time I can save a bit of waste. Depends on how tight I need to squeeze 'em. These chasers cut 15thou deep on each pass. If you were cutting these with a single point tool you would cut 5 thou. So you have to hold the feedstock pretty tight. I've only ever used a pair (or more) of nuts locked onto the threaded end and held in the three-jaw. Then again, I'm only an electronic engineer! Edited January 29, 2015 by stillp Quote Link to post Share on other sites
Grahamgl Posted January 30, 2015 Report Share Posted January 30, 2015 Why not screw the stud into a threaded mandrel? Graham Quote Link to post Share on other sites
AlanT Posted January 30, 2015 Author Report Share Posted January 30, 2015 I considered this. But all these methods, that rely on thread, wind up with the part having some runout or axial misalignment. Remember the die-head is essentially floating. So if the end is wobbling it cuts a wobbly thread. I am cutting these to within 1thou of the specified PD, rather than the usual practice of making bolts a bit small, so they fit any nut. Quote Link to post Share on other sites
AlanT Posted February 12, 2015 Author Report Share Posted February 12, 2015 (edited) Weather warmed up a bit so these got finished: https://flic.kr/p/r7amkw These are about 0.3in longer than a standard stud and made to a drawing by Mick Richards, "Motorsport Mickey". Presumably he knows that they fit if you do this! It becomes very obvious that a 3/8 UNC thread is much more likely to work in alloy than the original. Edited February 12, 2015 by AlanT Quote Link to post Share on other sites
Motorsport Mickey Posted February 12, 2015 Report Share Posted February 12, 2015 (edited) The trailing arms are generally short of material in every plane except down the length of the shank of the hub studs. Often the lugs cast onto the side of the hub dia dimension on the trailing arms are not well positioned to the extent that I've seen helicoils to take a 5/16th UNC thread (inner) break through the sidewall thickness. It makes sense that where extra material is present on the trailing arms you drill the holes deeper and utilise the virgin undrilled material to take a thread. Like Alan says there is at least another .3 or 5/16th of an inch material available on the studs centres. So the extra length studs can be tapped into that, also benefiting from the 3/8th UNC thread smaller dia into the alloy and the extra retained material rather than fitting the larger 5/16th UNC Helicoil with it's larger required drilled hole dia. Thanks Alan looks like an brilliant job, you've achieved an excellent finish on the threads and where the two different dias coincide the threads transorm from one dia into the other without any abrupt thread stop or changes which can cause stress points. Mick Richards Edited February 12, 2015 by Motorsport Mickey Quote Link to post Share on other sites
AlanT Posted February 12, 2015 Author Report Share Posted February 12, 2015 This EN8 steel is not great stuff to machine. It tears a bit. So the finish on these is not really very shiny. Not like it would be with free-cutting steel. But actually a shiny finish on a thread is not of much use. They are tough I would think. A die-head comes to a stop in four places each a little deeper. I cut away about 1 turn of the 3/8in thread using a radiused 45degree tool, so as to try and not leave a weak spot in the middle. Originally I expected to be able to cut these from one end, turning away the 3/8 thread to leave the 5/16 part. But , by a small fraction, a 3/8 thread is just too deep to allow this. So I had to cut from both ends. Got enough material left for a few more sets. Quote Link to post Share on other sites
TR NIALL Posted February 12, 2015 Report Share Posted February 12, 2015 Great Job once again Alan,it's Great to have Fellas like yourself on here for the Benifit of others who could not have achieved this type of Work. Quote Link to post Share on other sites
AlanT Posted February 12, 2015 Author Report Share Posted February 12, 2015 (edited) Thanks for that Niall but actually many TR owners could do something similar. Nor would it be very expensive these days. My lathe is 45 years old and I paid £200 for it. That would be 2 months salary at the time. But you could get a suitable machine for £200 today. A new diehead would be £850 today. But the one in the video came from ebay for £50 or so. The lathe motor amazes me. My Dad bought it used, from a junk shop in about 1960. Made by Crompton-Parkinson, very possibly before or during WW2. He used it to make an electric lawn-mower which we used for 15 years. I gave it away once. But then the guy gave it back. It runs cooler and quieter than all my "modern" ones. In lathe service it must have made ten thousand start-stop cycles. Edited February 12, 2015 by AlanT Quote Link to post Share on other sites
TR NIALL Posted February 13, 2015 Report Share Posted February 13, 2015 Haha Alan, anyone can Buy anything on eBay but it's having the ability to use what you've bought that duz the TRick. Quote Link to post Share on other sites
AlanT Posted February 13, 2015 Author Report Share Posted February 13, 2015 There was very little skill needed on these studs. The die-heads are automatic. The skill would come in if you tried to cut them with a single-point tool as is common on lathes. This method is OK for a one-off, especially if its a big one. But for a batch UGH!. its stopping in the right place in two directions thats a pain. Then you got to do it twice on each part!! It's mostly like this on a lathe. There is usually a tool that makes the task a breeze, if you have it. Quote Link to post Share on other sites
AlanT Posted February 14, 2015 Author Report Share Posted February 14, 2015 (edited) A die-head has quite a big range of adjustment for the diameter. So if you need to make non-standard sizes you can. These studs could have been cut to fit the hole left by a Helicoil tap. Of course this means you need to have a way to set them. You could just do it by trial and error with an ordinary nut. I used a standard thread gauge: https://flic.kr/p/rbgv4H And an thread micrometer, these measure the "effective" or "pitch" diameter directly. The thread charts give this as 0.2854in for a 5/16 UNF. https://flic.kr/p/r976HQ Its quite interesting to check ordinary production bolts. These are typically made 5 thou under-size. Here is a stud following a dip in phosphoric acid. This leaves a grey, protective phospate coat and the fizzing shifts bits of swarf and such. https://flic.kr/p/qTYD2x Finally here is an original" 5/16in both ends" stud. You will see now why these strip out the alloy so easily. The reason we have UNC and UNF threads is to suit alloy and steel. https://flic.kr/p/qTRSVS (photo from Mickey) Edited February 14, 2015 by AlanT Quote Link to post Share on other sites
Grabea Posted February 24, 2015 Report Share Posted February 24, 2015 Agreed the studs in my Triumph T100 engine from 1956 are BSW into the alloy and BSF for the nuts, more good old British engineering! Graham Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.