Ken Ratcliffe | 02/11/2020 14:35:26 |
25 forum posts 2 photos | Hi All, I am trying to cut an 8tpi thread in a 5/32" diameter silver steel bar. I am using free cutting silver steel as the instructions suggest. I have ground an ACME tool in HSS and have a live centre and travelling steady for support and turning the lathe by hand......but tool keeps catching (digging in) and warping the bar. Any thoughts or suggestions, as always welcomed ! Ken |
Clive Brown 1 | 02/11/2020 14:47:56 |
1050 forum posts 56 photos | How long is the thread? 5/32" dia. steel is very flexible for a cutting width of ~1/16" Could you try a narrower tool and 2 passes, shifting over after the first pass to get a full width cut? Lots of lubricant aswell. |
JasonB | 02/11/2020 14:53:10 |
![]() 25215 forum posts 3105 photos 1 articles | 8tpi ACME on 5/32" rod will be almost impossible as the depth of the thrad is far too great, either the 8 or the 5/32 is wrong |
David Davies 8 | 02/11/2020 14:54:30 |
![]() 202 forum posts 1 photos | 8 tpi ACME thread has a depth of 0.062. if you are cutting this in 0.156 stock that leaves a core of 31 or so thou. Something isn't right? |
David Davies 8 | 02/11/2020 14:55:28 |
![]() 202 forum posts 1 photos | Too quick Jason! |
Clive Brown 1 | 02/11/2020 15:04:25 |
1050 forum posts 56 photos | Doh! should've spotted that |
Ken Ratcliffe | 02/11/2020 15:10:58 |
25 forum posts 2 photos | Hi All, It is "only" 3/4" long thread. Just checking the instructions and it is 8tpi and 5/32" stock, it suggests a depth of 0.05" for the cut.....and fully admits it isn't going to be easy ! Maybe I should explain what it is for, it is a worm drive on a clock, so the thread drives a wheel, so, the depth of cut only has to allow wheel to engage, hence 0.50" cut. The book also suggests a tip on the acme tool of 1/32", again maybe not standard. I think I will give Clive's suggestion a go and lots of shallow cuts from reading around Ken |
MadMike | 02/11/2020 15:15:50 |
265 forum posts 4 photos | As Jason pointed out the core diameter will present problems in cuttink an 8TPI Acme thread. Even with your depth o.050 the core is still only .056 diameter. |
David Davies 8 | 02/11/2020 15:16:04 |
![]() 202 forum posts 1 photos | You could try cutting an 8 tpi 55 or 60 degree thread first then cleaning it up with the ACME tool. HTH Dave |
JasonB | 02/11/2020 15:24:22 |
![]() 25215 forum posts 3105 photos 1 articles | It will almost need a solid bush type traveling steady as you see on "running down" cutters. Rather you than me, at least it was easier to draw this is to the 0.05" depth and with 1/32" tool tip
Edited By JasonB on 02/11/2020 15:24:57 |
Mick B1 | 02/11/2020 15:30:08 |
2444 forum posts 139 photos | There'll be a larger helix angle - I think much larger - requiring a lot more side clearance, too, if the thread's got to advance 1/8" on a 5/32" OD. |
Ken Ratcliffe | 02/11/2020 15:35:44 |
25 forum posts 2 photos | I think I will try the 650 degree and then clean up......here is a photo from the build book, clearly better lathesmiths than me - but then again I thought making a wheel was impossible the first umpteen times I tried and messed up, I can usually get them first time now Ken
|
John Baron | 02/11/2020 16:22:36 |
![]() 520 forum posts 194 photos | Hi Guys, FWIW the laser head drive thread on a CD drive is very close to that size !
|
David Noble | 02/11/2020 16:49:16 |
![]() 402 forum posts 37 photos | Hello Ken, Which clock are you making? It looks very tricky David (Edit) Ah, sorry, just seen your other post. The Merlin Band Clock. Edited By David Noble on 02/11/2020 16:50:58 |
Martin Kyte | 02/11/2020 17:06:59 |
![]() 3445 forum posts 62 photos | A mate of mine (sadly deceased) obtained a drive thread for this clock from a bloke in Italy a couple of years ago. Maybe someone out there will have details. I do remember looking at it at the time and feeling quite thankfull I didn't have to cut one. I'm clearing his workshop at the moment, or was until the lockdown announcement, but I hav'nt come accross it yet. If there is more than one I will let you know. I'm sure the trick is in the design of the travelling steady. regards Martin |
Ken Ratcliffe | 02/11/2020 17:07:00 |
25 forum posts 2 photos | Yep David, it is the trickiest yet, for sure. Putting my lathe skills to the test. That and a traction engine on the go ! |
Martin Kyte | 02/11/2020 17:12:39 |
![]() 3445 forum posts 62 photos | Aha found it. Scroll down the page and you will see it on offer for 49 euros plus 12 euros postage. regards Martin |
Ken Ratcliffe | 02/11/2020 17:49:56 |
25 forum posts 2 photos | Thanks Martin, just dropped them a note. Much as I hate not making, this one could be beyond me - and the rest of the clock isn't easy ! |
old mart | 02/11/2020 19:18:38 |
4655 forum posts 304 photos | It sounds like it needs a tiny centre in the free end and a little centre to support it. |
JasonB | 02/11/2020 19:39:27 |
![]() 25215 forum posts 3105 photos 1 articles | The photo seems to show the rear toolpost being used as a traveling steady, possibly a half round cutout in the end of the support, topslide set at 90deg to lathe axis to put on the cut. As I said another option would be to mount a bush on the cross slide to support the work and again use topslide at 90deg to put on the cut. |
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