Machining mess with happy ending - Page 1
Forum section: electronics / general

author: soldar
author_rank: Super Contributor
timestamp: March 22, 2019, 11:50:07 am
content: I wanted to tap the inside of a brass plumbing fitting with 3/8" BSP thread. Brass is quite soft and I have the tap so I just started doing it but it was just not going well. Too much force was required. So, not having a lathe, I put the fitting on my drill press and used it to keep the tap aligned with a dead center but not to turn the tap which I did by hand with a wrench. After over three hours since I started the work I had completely destroyed any possibility of having a thread there because I had removed so much material there was no material left for a 3/8 thread. It was just a cone of greater diameter than the thread I needed. I guess the reason for the failure was that the tap was not perfectly aligned with the part and at a certain point it could not go in any further and it just removed whatever threads it had made. Oh well. At this point there was not much else to do than put everything away and forget the project.After putting everything away, I noticed I had been working on the wrong end of the fitting.I actually wanted the thread on the other end!So I got everything out again, put the fitting in the drill press with the right side up, started turning the tap and in a few minutes I had a perfect thread. Yay!

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2019, 11:56:07 am
content: Well doneTapping a thread can be very frustrating when it does not go right. I want to create very fine M58 x 1mm internal threads and have to use a lathe for that. I am not looking forward to that job !Fraser

author: Rerouter
author_rank: Super Contributor
timestamp: March 22, 2019, 12:11:07 pm
content: Its where having a threadmill is nice some times, if you have everything aligned correctly you don't have to worry about breaking taps.Still a pain getting everything concentric, but its the price you pay for not having to try and machine a reverse thread in a snapped tap when it breaks in the worse place possible.M58x1, I see your a man who enjoys pain, you must have a big lathe, or big balls, not sure which yet.

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2019, 12:58:18 pm
content: The lead-in taper looks too short to be a first (starting tap), it looks like a second or even finishing tap. I think that was your problem, trying to take too out much metal in too short a distance with no thread form to pull it in. You did well!

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2019, 01:01:01 pm
content: Quote from: Fraser on March 22, 2019, 11:56:07 amThe right lubricant for the material you're tapping makes a massive difference, especially with fine threads. You don't want anything galling and sticking to the tap.

author: soldar
author_rank: Super Contributor
timestamp: March 22, 2019, 02:17:18 pm
content: Quote from: Gyro on March 22, 2019, 12:58:18 pmI think you are right. I know taps come in sets of three but this is the only one I have so I had to make do. Maybe next time I can grind the opening a bit wider to make it easier for the tap to get in and get aligned.Yes, having the right tools makes any job much easier but sometimes I just have to get by with what I have at hand.I guess it was lucky that I messed up at the wrong end of the fixture and had a second chance at the correct end and completed that successfully. In spite of the hours I wasted I guess "all's well that ends well".I used some motor oil as lubricant and was careful to advance a bit and then back out a bit. Using the drill press to put pressure and keep the tap centered was great help. I do not think I could have done it free hand. I have tapped some smaller screw threads in the past but never anything this size. I can't even think of doing a M58 x 1.I need to get a lathe but the cost, not only of the lathe but of all the accessories, gives me pause.

author: noidea
author_rank: Unknown
timestamp: March 22, 2019, 02:50:13 pm
content: Quote from: Fraser on March 22, 2019, 11:56:07 amFor an internal thread like that try running in reverse with the tool mounted upside down and cutting on the backside away from the chuck. There's a good tutorial here, but you would have to grind your own tool for something that small:https://youtu.be/k1DHKjMtdQw

author: langwadt
author_rank: Super Contributor
timestamp: March 22, 2019, 03:40:38 pm
content: Quote from: noidea on March 22, 2019, 02:50:13 pmupside down or reverse not bothand be careful if you have lathe with a screw on chuck

author: soldar
author_rank: Super Contributor
timestamp: March 22, 2019, 03:53:38 pm
content: Quote from: langwadt on March 22, 2019, 03:40:38 pmHeh, I thought I had seen the same idea in some other video. After some searching I see it's the same guy.E.T.A: This one is making an outside thread by cutting it away from the headstock.

author: noidea
author_rank: Unknown
timestamp: March 22, 2019, 04:35:51 pm
content: Quote from: langwadt on March 22, 2019, 03:40:38 pmWoops I don't know what I was thinking when i typed that (doh...) . My lathe has a screwed on chuck so I must admit I've never actually done it myself.

author: soldar
author_rank: Super Contributor
timestamp: March 22, 2019, 05:24:16 pm
content: Not too long ago I saw a video on Youtube about turning on the lathe with the tool facing down and the lathe running backwards.The problem they were trying to solve is that the material, maybe brass, did not produce a nice strip like ferrous alloys do but it produced tiny chips which went flying everywhere. By turning backwards and the tool facing down the chips flew downwards and into the tray rather than upwards and into the machinist's eyes.I cannot find the video now but I think it was one byThis Old Tony.E.T.A.: here it is at about 7:15https://youtu.be/PFqjQ3l1MRA?t=438