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Post by kagetsume on Nov 29, 2021 13:44:27 GMT -5
I've for an Eastwood 7x12 Mini lathe (that I've upgraded bearings on, gibs, quick tool post, etc). It in general works really well for me, except for long boring tasks (bores greater than 1-2 inches). Whenever I try to use a longer boring bar to widen out a tube (say for inches or more in length), the inside of the bore looks awful; severe chatter, the walls end up all ridged, and nothing is smooth at all. I was wondering if anyone here has experience on doing long bores on these small lathes and how to actually get a smooth long bore.
I've tried numerous types and diameters of boring bars to no success.
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Post by Vektor on Nov 29, 2021 15:04:34 GMT -5
For me it's usually been up to two things: speed and tool tip contact point.
I usually get the best result at low rpm and thus low advance speed as well. The finishing passes always need power feed, manual feeding rarely results in particularily smooth finish. Also the finishing cuts need to make only very light contact, I actually keep the X axis untouched for 4 or 5 final passes.
In my current lathe, similar frame as yours, the better one of my boring bars is a bit too slim and hence it vibrates like crazy when I bore deeper. But I've managed to eliminate a lot of that by tilting the tool in the holder so that the tool tip don't contact the ID wall at center level, but a great deal lower. I'd say mine is angled about 15 to 20 degree lower. In my previous CNC lathe I actually had the boring bar tool tip pointing almost straight up, giving best result.
EDIT: I do have to add that I rarely bore over 2 inches deep! I've noticed depth beyond that not only needs insanely strong boring bar, but I'd probably also need a steady rest. And I hate steady rests, I've never got them to work as they should in none of my lathes. For really deep boring, a right sized blacksmith's drill bit might work better.
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Post by Obi-Shane on Nov 29, 2021 20:18:37 GMT -5
Do you have a picture of what your boring bars look like? Insert or hss? Is your tool height set correctly? Some insert boring bars are kind of funky and have a funny angled engagement.
I was about to say your issue is the lack of chip evacuation and that's what causing your bad surface finish but you mentioned chatter and that comes from tool pressure or too much cutting edge engagement. Could be a few things at work here such as how the part is chucked up as well. Yeah, shoot us some pics and maybe something will stick out to us.
When I bore, I prefer to always use some kind of coolant, it helps with chip build up which can quickly ruin your finish. When I bore I use the thickest boring bar I can for that hole, thicker the more rigid, and only have as much stickout as I have to to reach my depth. I never get chatter when I bore, but I do get singing when doing "thin parts" , which is normal but also comes from deflection.
A video that covers a few things. (Never watched this guy before)
The reason why his spring pass towards the end gave him a horrible finish compared to the deep cut before that is because the depth of cut doesn't overcome the radius of the cutting edge on the insert. And it just rubbed off a few thou. There's technically a minimum depth of cut for these things.
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Post by nosloppy on Nov 30, 2021 2:49:58 GMT -5
I want to be a wise guy and answer the thread with "Sounds like my Ex wife."
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Post by Obi-Shane on Nov 30, 2021 4:28:16 GMT -5
I want to be a wise guy and answer the thread with "Sounds like my Ex wife."  |
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Post by kagetsume on Nov 30, 2021 9:53:02 GMT -5
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Post by Nerf Herder on Nov 30, 2021 16:42:57 GMT -5
I used a custom ground (by me) HSS insert in the boring bar on my old lathe, and got a beautiful finish on my id's.
I've tried the same setup on my new lathe of the same size with zero success, but I'm still breaking in the lathe.
Somehow the manufacturer decided the best design is with rubber pads under the feet of the lathe, which causes vibration to magnify like the ripple effect of skipping a rock across a pond.
You could always bore from both ends of a part to achieve the depth you need. It isn't ideal, but it gets you there.
I know some guys have actually wrapped multiple thick rubber bands around the bar and post/holder with a bit of success.
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Post by Nerf Herder on Nov 30, 2021 16:48:20 GMT -5
Aaand I just looked up that lathe model. Sieg clone, same as mine. Check to see if it also has those rubber pads on the feet.
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Post by kagetsume on Nov 30, 2021 20:15:38 GMT -5
Yup, it has the rubber feet.
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Post by kagetsume on Nov 30, 2021 20:24:53 GMT -5
And yeah, it's a Sieg clone. I've done several of upgrades to it.
Replaced steel saddle gibs with brass for smoother movement.
Replaced cross-slide gibs with brass (same reason, smoother movement).
Replaced headstock bearings with much improved ones.
Replaced basic 3" chuck with a 4" six-tooth chuck specifically for gripping cylinders more evenly
Replaced tool post with a quick-change toolpost (wedge style, not piston).
Got a bearing-based steady for longer tube work. This does help.
Disassembled almost the whole thing and reset/retightened everything (which fixed some leadscrew issues I had) as well as cut the backlash the slides had by a lot.
For OD work and facing, I can get great finishes, nearly mirror depending on the tool I use. It's just the long bores that are giving me absolute fits. Maybe I'll replace the feet with solid and put the whole thing on an anti-vibration neoprene mat to see if that helps any further.
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Post by Nerf Herder on Dec 2, 2021 9:44:21 GMT -5
As a short term fix until such time as I'm able to remove those rubber things, I wedged a piece of stock almost the exact same depth between the surface of my work bench and the chip tray. It removed the vibration sufficiently for basic external turning, but I will have to tear those feet off and mount it properly (I've only been running it for 3-4 weeks now).
Please keep us posted on your progress with this.
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Post by Obi-Shane on Dec 2, 2021 21:18:37 GMT -5
And yeah, it's a Sieg clone. I've done several of upgrades to it. Replaced steel saddle gibs with brass for smoother movement. Replaced cross-slide gibs with brass (same reason, smoother movement). Replaced headstock bearings with much improved ones. Replaced basic 3" chuck with a 4" six-tooth chuck specifically for gripping cylinders more evenly Replaced tool post with a quick-change toolpost (wedge style, not piston). Got a bearing-based steady for longer tube work. This does help. Disassembled almost the whole thing and reset/retightened everything (which fixed some leadscrew issues I had) as well as cut the backlash the slides had by a lot. For OD work and facing, I can get great finishes, nearly mirror depending on the tool I use. It's just the long bores that are giving me absolute fits. Maybe I'll replace the feet with solid and put the whole thing on an anti-vibration neoprene mat to see if that helps any further. Yikes, Sounds like a import lathe issue. Clint. you got this one. |
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Post by kagetsume on Dec 2, 2021 23:03:58 GMT -5
Bear in mind I did the above upgrades to improve on the lathe. It worked well without them on turning, the above just dialed it in a lot further/made movements smoother. They're a set of recommended upgrades to the Sieg clones.
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Post by Guylo Ren on Dec 4, 2021 4:22:28 GMT -5
I too have encountered the same problems with boring,ie chatter & bad finish,hence multiple failed emitter ID cuts- & I was using the big lathe at work.Was both advised & came to the conclusion that I obtained a better finish with slightly deeper cuts.
This would seem to be in line with Shane's advice- by not overcoming the cutting radius of the tool,it felt like the tool was just skipping across the material surface without really cutting,thus ruining a perfectly good finish up to that point.
I seemed to encounter this issue more so with ID than when turning OD- tool chatter still occurs sometimes but seemed more common when using a boring bar.As beefy a bar as possible can help minimise the effect too,as it'll have less flex,but that of course is relative to the size of hole you're opening out.
Somewhere between challenging & maddening,this stuff!😬
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Post by Obi-Shane on Dec 5, 2021 23:34:06 GMT -5
Bear in mind I did the above upgrades to improve on the lathe. It worked well without them on turning, the above just dialed it in a lot further/made movements smoother. They're a set of recommended upgrades to the Sieg clones. Yeah, I believe you. I've seen a few videos on the sieg clone vids that line up with what mods you did on your lathe to improve it. |
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Post by Obi-Shane on Dec 7, 2021 22:08:44 GMT -5
I too have encountered the same problems with boring,ie chatter & bad finish,hence multiple failed emitter ID cuts- & I was using the big lathe at work.Was both advised & came to the conclusion that I obtained a better finish with slightly deeper cuts. This would seem to be in line with Shane's advice- by not overcoming the cutting radius of the tool,it felt like the tool was just skipping across the material surface without really cutting,thus ruining a perfectly good finish up to that point. I seemed to encounter this issue more so with ID than when turning OD- tool chatter still occurs sometimes but seemed more common when using a boring bar.As beefy a bar as possible can help minimise the effect too,as it'll have less flex,but that of course is relative to the size of hole you're opening out. Somewhere between challenging & maddening,this stuff!😬 Yeah dude, cutting radius and minimum depth of cut is a real thing. And the cutting Pressure needed to actually get a cut. Cutting pressure is a HUGE thing that should be factored in. I wouldn't lie to you guys. Sometimes (Most of the time, at least for the tolerances we deal with in our lightsaber world) You can cheat it, but the surface gets all chowdered up. Technically speaking none of us should probably be using these traditional sintered inserts, but it's so convenient. Try and grab some ground ones, I have several and love them now. I can post pics maybe. Sharper the better, for our lathes at least. But in a CNC production environment they won't last very long, and that's mainly what inserts were designed for. I recommend checking out these videos for a deeper understanding on the matter, I found them very informative. Honestly I recommend watching all his lathing videos, He's knows his stuff. Most of that video is about the machine and how he built it, but the goes into why a few times and explains a few important things. I've watched most of his videos, several of them more than a few times, especially the lathing ones. There's always a take away I find. It can be a bit maddening I guess, but it's also a art form in itself. and can be quite rewarding. Oh and even if you watch Abomb, who's been doing this all his life and is a third generation machinist. He'll get to machining something, and sometimes he's just not getting the results he wants and starts swapping out inserts and/or adjusting his feeds and speeds til he gets what he wants. So, even he doesn't get it perfect the first time. Speaking of which, back to Clint and kagetsume 's chatter issue. What spindle speeds are you running? These new lathes like the Sieg clones are usually much higher speed capable and most people take advantage of that. I wonder if dropping down your spindle speeds a bit might help. Stepping down as you go to see what results you get. |
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Post by kagetsume on Dec 7, 2021 22:43:28 GMT -5
The high speed gear runs it at around 2200rpm max I believe.
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Post by Obi-Shane on Dec 7, 2021 23:14:07 GMT -5
The high speed gear runs it at around 2200rpm max I believe. Are you running that high when you are boring? If so that's pretty high, actually yeah, that's very high especially if you are using a steady. Every time I see guys use steady rests they have their speeds turned down with copious amounts of oil on the steady jaws, if they don't have rollers equiped. Try and drop it down to 500-700 and see what happens. Play with it a bit and see what she does. Don't use the powerfeed and see if you can feel with your hand what the cutter is doing and how it responds to the depth of cut and your feed as you advance it. I'm doing most machining operations at 750 rpm ish. Parting at 450 ish. It's tricky because we are using two completely different machines but the same physics apply I would think. |
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Post by Nerf Herder on Dec 8, 2021 9:04:14 GMT -5
Speaking of which, back to Clint and kagetsume 's chatter issue. What spindle speeds are you running? These new lathes like the Sieg clones are usually much higher speed capable and most people take advantage of that. I wonder if dropping down your spindle speeds a bit might help. Stepping down as you go to see what results you get. On old faithful, I would run my rpm's around 250-300 (using a HHS cutter I ground) for boring, and Lot's of WD40. Like, totally soaked. The HSS seemed to bite harder and was more forgiving if the tool height was slightly off. Plus, I could hone the radius and/or knock tiny burrs off the cutter with a flat file in seconds mid-session.
My old steady rest has solid brass jaws, no rollers. Again, soaked it with WD before spinning under power. Then again about every 3-4 passes. When I first got the setup (used... And me as a total newb) the chamfers on the jaws were more crisp and my work suffered because of it. After running a dozen or so pieces through it, the brass rounded off and settled in. As it was when I retired it, it left virtually zero tool marks in a work piece, or at least - nothing some sandpaper and WD40 @ 600rpm for 60 seconds couldn't sort out.
So far I've only done external turning on my new rig mostly. What little boring I have done has been a fail (even clean up cuts/spring passes) at anything above 150rpm due to the rubber feet. I really have to get those off the lathe.
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Post by kagetsume on Dec 8, 2021 23:20:02 GMT -5
Okay, so ... I am not listening to my friend anymore on speeds to run at. He's got a Sherline mill and always recommends 'run as fast as possible'. Yeah, well, he's utterly wrong! I dropped my lathe to low gear, and then went to 1/3 (which is about 300ish RPM). I didn't even bother to center the piece extensively (I usually use a gauge to set the runout as minimal as possible and then lock a steady if i need it for long bores. Well, I just chucked it in, set it in the steady at the last setting ... and did one of the best 3+ inch bores I've ever managed. It's not 100% smooth (some slight ridging), but nothing one of my manual reamers couldn't clean up in a couple of easy passes. I used both my thicker and thinner boring bars. Had virtually no vibration, no chatter at all. Did the tool move all by hand too (no leadscrew power). It's 1000% better. So, I was mostly just running way too fast. Low gear (high toque), 1/3 speed, and I can get the boring I need so much easier. Man, wish I knew this before I went through several tubes and lots of cussing.  |
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Post by kagetsume on Dec 8, 2021 23:25:41 GMT -5
And FWIW, my HSS triangle boring bar was cleaner than one of the carbide insert ones. But either is more than passible since the manual reamer can clean up with a final couple passes to make a really smooth inner bore.
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Post by Obi-Shane on Dec 9, 2021 6:49:04 GMT -5
Okay, so ... I am not listening to my friend anymore on speeds to run at. He's got a Sherline mill and always recommends 'run as fast as possible'. Yeah, well, he's utterly wrong! I dropped my lathe to low gear, and then went to 1/3 (which is about 300ish RPM). I didn't even bother to center the piece extensively (I usually use a gauge to set the runout as minimal as possible and then lock a steady if i need it for long bores. Well, I just chucked it in, set it in the steady at the last setting ... and did one of the best 3+ inch bores I've ever managed. It's not 100% smooth (some slight ridging), but nothing one of my manual reamers couldn't clean up in a couple of easy passes. I used both my thicker and thinner boring bars. Had virtually no vibration, no chatter at all. Did the tool move all by hand too (no leadscrew power). It's 1000% better. So, I was mostly just running way too fast. Low gear (high toque), 1/3 speed, and I can get the boring I need so much easier. Man, wish I knew this before I went through several tubes and lots of cussing. Boom! That's how it's done. Glad I could help. Yeah, you're buddy is giving you some really bad advice. As I was running an op on my lathe the other day I swapped my speed down from my usual 750 to 450 for a large diameter op and it dawned on me you never mentioned your spindle speed. "Ludicrous spindle speeds" are a bit of a selling factor with new lathes so maybe people think it's better. And then it also dawned on my that Clint was also having the same issue but only after he transitioned from an old lathe to a new one. Old lathes rarely go above 1k rpm so he wouldn't have had this issue by default. So what could be the problem if he's just doing what he did before? Keep us posted Nerf Herder. This is why videos are so handy, when someone asks for help. The simplest solution to a problem is so easily overlooked. Yeah dude, one step of the problem solved. Now to dial it in some more and you won't be messing with the reamers. |
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Post by Guylo Ren on Dec 9, 2021 8:20:24 GMT -5
Yeees,great job kagetsume!After reading what you guys wrote the last few days,I discussed the issue with one of my friendly neighbourhood toolmakers at work & straight away he said, 'OH yes- drop the RPMs down for boring out your ID."
If I'd known the right questions like this to ask over the last 18 months,I might not have wound up with the ratio of 3 failed Jedi Killer hilts to 1 successful!
This thread & discussion is invaluable to us all on here who are currently making,so glad to be on board!👍🏻👍🏻
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Post by Nerf Herder on Dec 9, 2021 8:22:49 GMT -5
Teamwork makes the Dream work! Hazaa!
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