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15th Sep 2019, 10:41 PM #31
Thanks for the tips Pipeclay. OK, so maybe the 4140 I was given will be OK to use ?
I can run my lathe in reverse thanks to the VFD, but I am worried about the chuck unscrewing from the forces generated. I have screwed the chuck on and off multiple times lately, today I was making some aluminium components for some pens I am making, I turned the switch off and the chuck started to unscrew by itself. I have the VFD setup to stop the rotation in 2 seconds. ( This is the first time its come loose on me, not put on tight enough when I put it back on last time obviously, but proves it can happen )
I like the idea of having that runout space at the end of the thread, I think this is probably how I will do it. I can run the lathe at very low rpm, so that and the runout space should make things safe enough.
Do the carbide inserts cut OK at these very low speeds ? ( 30-60rpm )Brad.
Every Day might not be a good Day,
but there is something good in every Day.
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15th Sep 2019, 10:43 PM #32
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15th Sep 2019, 10:45 PM #33Philomath in training
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15th Sep 2019, 10:47 PM #34
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15th Sep 2019, 10:51 PM #35
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15th Sep 2019, 10:56 PM #36
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16th Sep 2019, 12:14 AM #37
Hi Brad, Guys,
I use carbide insert threading tools, only because I seem completely unable to grind HSS tools to the correct angles for threading. I tend to run at about 100 rpm until I'm sure that the thread is correct, and then higher speeds to finish.
I also plunge cut threads which seems to be frowned upon by some. I know and understand the reasons why, but for the threads that I cut, which tend to be relatively small ones its just fine. At the end of the day if it works for you, fine, go with it and don't fret about it.
I consider myself a rank beginner and I'm still learning, so if you are happy with what you are doing and achieving, then carry on.
26-08-2019-005.jpgBest Regards:
Baron J.
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16th Sep 2019, 07:44 AM #38Philomath in training
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I have a small fixture I use to grind HSS to correct angles, similar to this https://metalworkforums.com/f65/t188...99#post1806599
If you go the way I did on post 30, I could grind a small piece of HSS to a 60 degree angle for you.
Michael
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16th Sep 2019, 10:05 AM #39
If I already had the insert tooling, I would go that way. But it means finding the right stuff on the internet and waiting for it to arrive.
I did the dummy shaft thread by plunging.
I am pretty confident I can grind a cutting tip to do the job. Making a bar to hold it is more my issue I think.
Do I drill a hole through a piece of bar and tap a hole for a grubscrew to hold it in place, or do I silver solder it to the end of a bar.
I also have the issue of not having a boring bar suitable to do the hollowing out, and to cut the runout section at the end of the thread.Brad.
Every Day might not be a good Day,
but there is something good in every Day.
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16th Sep 2019, 10:18 AM #40
Sorry, I missed this post. I have my settings at 30 posts to a page, you must have slipped it in as I was replying and things went over to page 2.
That looks like something I have been dreaming up, though I would be worried about the end of the bar hitting the end of the hole, I would have to chop it off closer to the cutter.
The tape is something I do all the time on drill bits etc. though usually put a mark with a paint pen.Brad.
Every Day might not be a good Day,
but there is something good in every Day.
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16th Sep 2019, 12:40 PM #41Golden Member
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- Oct 2008
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- Cairns, Q
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Hi BaronJ
I use one of these:
https://www.carbatec.com.au/jig-chisel-grinding
They are fairly flimsy, but adequate for the purpose. They come with paper templates to make gauges to give the correct table tilt for various chisel bevels using a 150 mm grinding wheel. I made similar templates from 40x3 aluminium to give the correct front, side and top rakes needed for HSS lathe tools.
Frank.
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16th Sep 2019, 01:22 PM #42
Not going too well with the 4140. I am using a Diamond toolholder from Eccentric Engineering.
First up, I chucked up the bigger piece ( 67.5mm x 100mm long ) and took a light skim cut off the end, things were going OK, I thought it cut pretty much the same as the piece I used for the dummy shaft.
DSC_0281.jpg
I then put the smaller piece ( 62.5mm x 75mm long ) in the chuck and proceeded to do the same thing. It started off OK, but the tip didn't last long ( 1/4" CoHSS )
DSC_0279.jpg
I had a freshly sharpened piece of 1/4" Tantung, I swapped over to that, it didn't last much longer. This piece could have benefited from having the sides honed and a small radius put on the front edge, but I would have thought it would have done better than it did. This piece is much brighter than the first, no rust. On one end is the original bright blue paint , both are marked 4140 by marking pen.
DSC_0276.jpg
I was cutting dry, very light cuts like .1mm and .2mm. Slow feed by hand, lathe was doing an estimated 1000rpm.
Any thoughts on what I am doing wrong here ?Brad.
Every Day might not be a good Day,
but there is something good in every Day.
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16th Sep 2019, 02:30 PM #43Most Valued Member
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Increase nose radius slightly,drop speed to 500 or lower, use a cutting oil or coke bottle with hole in lid a solbile oil squirted occasionally, increase depth of cut to .005"/.010" for facing.
Turn OD at about 250/350 depth of cut around .020"/.040" feed rate around .002"/.003".
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16th Sep 2019, 08:45 PM #44
Thanks for the tips Pipeclay, I will give them a try when I get a chance to regrind the cutters. Might take me a week to get back to it now, work calls again unfortunately.
Brad.
Every Day might not be a good Day,
but there is something good in every Day.
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16th Sep 2019, 08:56 PM #45Philomath in training
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- Oct 2011
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This that same boring bar from my previous post, but this time loaded with a 55 degree shaped tool.
IMG_0606.JPG
The basic design is a bar with a cross drilled hole (shaped for the HSS cross section) and then a grub screw in the end to secure the insert. Being round in a standard tool holder, this one has a square profile holder that clamps the bar. (I have a larger one made of 25mm round bar that goes directly in a round holder, but still the same design).
If you were pushed for space, I guess you could put the grub screw in from the top (allow a shorter end), but the bar may have to be slightly larger in diameter to give the grub screw something to bite against.
Michael
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