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Post by tbenen on May 19, 2021 15:41:50 GMT -5
BEHOLD: AN EXAMPLE OF HOW NOT TO DO THINGS
I said I'd make one of these, and here it is! Riddled with mistakes and too long to be entertaining. I go over the whole process, minus some tedious stuff. I originally had time-lapses between the cuts, but I couldn't be bothered at this point. Enjoy!
Here's a picture of the final piece. Lots of banding, whatever. Still turned out okay!
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Post by Obi-Shane on May 19, 2021 17:03:57 GMT -5
Video still listed as processing for me for about an hour now. So I'll check back in this evening and see if it's done uploading.
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Post by tbenen on May 19, 2021 17:19:32 GMT -5
YouTube was being weird and pausing my upload without telling me, it is up now
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Post by Obi-Shane on May 19, 2021 19:43:55 GMT -5
I'm 15 min in and haven't seen you do any machining yet. You're talking about the build but that doesn't help me help you. You did do a few manual passes left and right (5:20 mark) when the lathe was on and I can tell you that you are moving your cutter WAY to fast.
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Post by Obi-Shane on May 19, 2021 19:58:25 GMT -5
Yeah, if you're going to do another video just do the machining and don't talk and I can see what's going on. Or I mean you can talk sheesh, but what I really need to do is see your depth of cuts and feeds and speeds.
Ok so what I can tell you right now is your tooling is much too large for your lathe, but I know why you do it and I do the same thing but try and work around it. The actual cutters are too large and want a much higher feed/speed/and depth of cut than your lathe is capable of, so don't expect to ever really get any chip breaking with a insert that large. Since the cutter shank is so large you are having to drop the tool holder down so far on your tool post to get on center that the piston is only engaging the top of the holder and pushing it away from the dovetail. Since you have a dovetail/piston style and not a wedge type, that means the engagement isn't so great and causing your tool holder to sit slightly canted in your tool post because of this. Make sense? Also you have a aluminum tool post, and from my experience those are pretty bad. I had one once. They aren't nearly as rigid as the steel ones.
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Post by Obi-Shane on May 19, 2021 20:14:05 GMT -5
And you are right. It's not the lathe, it's just growing pains on your setup. We've all been there. With Carbide, technically, not many of our lathes take any advantage of it. It's designed to go ludicrous speed and hog material off faster than you can move your hands and the machine can spin. If you aren't pressing the cutter far enough into the material you are doing more rubbing it off then cutting it off due the radius on the cutting edge (not tip radius), since the inserts are designed to move material fast and last in a production environment they need this radius. This also causes a lot of chatter because of the increased tool pressure, and effects your surface finish. They make cutters that are made specifically for cutting aluminum and they have a much sharper cutting edge. Which is a win/win for us hobby lathe guys. They much sharper edge which decreases tool pressure, and reduces chatter and the depth of cut needed.  You can see the cutting edges are a lot sharper. They also have a very positive rake to allow for easy material removal. This might sound like an odd comparison but its like a knife cutting a steak, sharper the knife the easier it is (less tool pressure), and cleaner your cut will be (surface finish). |
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Post by Obi-Shane on May 19, 2021 20:29:22 GMT -5
When setting up the part to go in your live center it should technically be faced off so you have your face is square to the work, if it's saw cut which it probably is, it will introduce run out. I realize this is impossible to do in your lathe, and probably mine with a piece that long, but it's important to be aware of.
You're collet also might be introducing something into the mix.
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Post by tbenen on May 19, 2021 21:40:25 GMT -5
Lots of stuff to go over! Yeah, I talked a lot. I left the "actual machining" out because I didn't feel like it made for a good watch, looking at power feed go and listening to gears. I wanted more of a process video as opposed to an in depth diagnosis type deal. Sorry if it was a frustrating watch! I have gotten good chips before, only when the work got up to a certain temperature as makes sense. I absolutely do not have the right inserts! Still working off of the first set I got my hands on. I figured bigger shanks meant more stable, but that just means oversized tools. I only hold out on carbide since I don't have a grinder for HSS sharpening. That might be a really good investment in the future... Big tools means too low, causing instability in the small tool post. CAM style alu tool post also not ideal. Got it! That's what I get for using cheaper tools on a medium sized lathe Sharp tools are better for alu since it is much softer. Some proper tooling is definitely in order. Both sides of the stock were faced! I actually had the stock prepped by Wanderlust Fabrication and Design. I'm a friend of the owner and he has an industrial sized lathe that makes short work of parting and facing stock.
Thank you for the analysis!
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Post by Nerf Herder on May 20, 2021 8:10:22 GMT -5
Lots of stuff to go over! Yeah, I talked a lot. I left the "actual machining" out because I didn't feel like it made for a good watch, looking at power feed go and listening to gears. I wanted more of a process video as opposed to an in depth diagnosis type deal. Sorry if it was a frustrating watch! I have gotten good chips before, only when the work got up to a certain temperature as makes sense. I absolutely do not have the right inserts! Still working off of the first set I got my hands on. I figured bigger shanks meant more stable, but that just means oversized tools. I only hold out on carbide since I don't have a grinder for HSS sharpening. That might be a really good investment in the future... Big tools means too low, causing instability in the small tool post. CAM style alu tool post also not ideal. Got it! That's what I get for using cheaper tools on a medium sized lathe Sharp tools are better for alu since it is much softer. Some proper tooling is definitely in order. Both sides of the stock were faced! I actually had the stock prepped by Wanderlust Fabrication and Design. I'm a friend of the owner and he has an industrial sized lathe that makes short work of parting and facing stock.
Thank you for the analysis!
For what it's worth, I used to work only with hss cutters, a few of which I ground myself. Obi Shane might not remember this, but he strongly encouraged me to take a crack at carbide and I haven't looked back since. One caveat, as pointed out, light cuts and spring passes are more likely to mar the finish. Carbide definitely prefers to bite hard and remove material. Those rings in the finish tell me that you have a lot of vibration going on. What is the work surface like, nice and thick/sturdy?
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Post by tbenen on May 20, 2021 11:17:11 GMT -5
For what it's worth, I used to work only with hss cutters, a few of which I ground myself. Obi Shane might not remember this, but he strongly encouraged me to take a crack at carbide and I haven't looked back since. One caveat, as pointed out, light cuts and spring passes are more likely to mar the finish. Carbide definitely prefers to bite hard and remove material. Those rings in the finish tell me that you have a lot of vibration going on. What is the work surface like, nice and thick/sturdy?
The table under the tarp in the video is one I made myself! The table top is reinforced, but the legs leave something to be desired. To be honest, I ran out of screws during the build. It doesn't move at all when being used as just a table, but you can push it to make it rock. Thinking back, the last hilt I remember turning without the banding was on a solid oak bench at a workshop I used to work in. I think you're on to something! Some cross braces (or more screws in some places...) might be a really good idea to install.
Question about carbide: A lot of people have their own preferences for the shapes of their carbide. I tend to be fond of the triangular ones because they've got three cutting points and allow for easy chamfering. What do you guys use?
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Post by Nerf Herder on May 20, 2021 12:58:15 GMT -5
Same. I had a right hand brazed carbide bit initially that was junk. Followed it up with a set of inserts and the difference is unreal. I do still use hss for threading. Carbide does seem to be too aggressive for that purpose.
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Post by Obi-Shane on May 20, 2021 18:23:01 GMT -5
Lots of stuff to go over! Yeah, I talked a lot. I left the "actual machining" out because I didn't feel like it made for a good watch, looking at power feed go and listening to gears. I wanted more of a process video as opposed to an in depth diagnosis type deal. Sorry if it was a frustrating watch! I have gotten good chips before, only when the work got up to a certain temperature as makes sense. I absolutely do not have the right inserts! Still working off of the first set I got my hands on. I figured bigger shanks meant more stable, but that just means oversized tools. I only hold out on carbide since I don't have a grinder for HSS sharpening. That might be a really good investment in the future... Big tools means too low, causing instability in the small tool post. CAM style alu tool post also not ideal. Got it! That's what I get for using cheaper tools on a medium sized lathe Sharp tools are better for alu since it is much softer. Some proper tooling is definitely in order. Both sides of the stock were faced! I actually had the stock prepped by Wanderlust Fabrication and Design. I'm a friend of the owner and he has an industrial sized lathe that makes short work of parting and facing stock. Thank you for the analysis!
For what it's worth, I used to work only with hss cutters, a few of which I ground myself. Obi Shane might not remember this, but he strongly encouraged me to take a crack at carbide and I haven't looked back since. One caveat, as pointed out, light cuts and spring passes are more likely to mar the finish. Carbide definitely prefers to bite hard and remove material. Those rings in the finish tell me that you have a lot of vibration going on. What is the work surface like, nice and thick/sturdy?
That's right, we did talk about that. Yeah, Carbide is just is the way to go imo. Rather then dealing with the hassle of learning how to grind, you can hit the ground running right out of the gate and start making stuff. And that's pretty much all I use, but it's very important to be aware of it's "issues" when working with it on our machines. I get really good surface finishes on alu, stainless steel, brass, 12L14 steel. I get horrible surface finishes on cold rolled steel, which is annoying since I have a lot of it. And copper, don't get me started on that. If you really wanna have a bad day, try machining pure copper. For what it's worth, I used to work only with hss cutters, a few of which I ground myself. Obi Shane might not remember this, but he strongly encouraged me to take a crack at carbide and I haven't looked back since. One caveat, as pointed out, light cuts and spring passes are more likely to mar the finish. Carbide definitely prefers to bite hard and remove material. Those rings in the finish tell me that you have a lot of vibration going on. What is the work surface like, nice and thick/sturdy?
The table under the tarp in the video is one I made myself! The table top is reinforced, but the legs leave something to be desired. To be honest, I ran out of screws during the build. It doesn't move at all when being used as just a table, but you can push it to make it rock. Thinking back, the last hilt I remember turning without the banding was on a solid oak bench at a workshop I used to work in. I think you're on to something! Some cross braces (or more screws in some places...) might be a really good idea to install. Question about carbide: A lot of people have their own preferences for the shapes of their carbide. I tend to be fond of the triangular ones because they've got three cutting points and allow for easy chamfering. What do you guys use?
So you got a good surface finish with the other table? Strange. Is the lathe bolted to the table or does it just sit on it? What I really need to see tho is you actually turning the piece and showing me what rpm's you are using and how fast your feed is. You might have crazy high rpms and a fast feed. Is there a singing sound when you do your finishing pass? Many questions. I use DCMT's and CCMT's mostly. I have one WNMG (6 cutting edges). My parting blade uses MGMN200 inserts. I've used the triangle ones before and they worked fine, it's smart to have something with several cutting edges. |
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Post by tbenen on May 20, 2021 20:09:29 GMT -5
So you got a good surface finish with the other table? Strange. Is the lathe bolted to the table or does it just sit on it? What I really need to see tho is you actually turning the piece and showing me what rpm's you are using and how fast your feed is. You might have crazy high rpms and a fast feed. Is there a singing sound when you do your finishing pass? Many questions. I use DCMT's and CCMT's mostly. I have one WNMG (6 cutting edges). My parting blade uses MGMN200 inserts. I've used the triangle ones before and they worked fine, it's smart to have something with several cutting edges.
Lathe is not bolted, just bolted to a piece of 1/2in MDF then sat on a table.
Dial on the lathe goes from 50 to 2500 rpm, not sure how accurate that is. I run that dial at maybe 60 to 70%? Questionably 1600 rpm, I've no way to measure it myself. I get to this value by messing with the speed during a power feed cut and listening. I try to avoid whining sounds or things that make the cut really high pitched and loud. Sometimes happens anyway, I assume that's what you meant by sing and I assume that it is not a good thing. Does sometimes happen on the lighter passes, happened a fair bit during the machining of the hilt in the video but only during the finishing of the big middle section where I was having vibration issues anyway so I didn't feel like it was abnormal.
In terms of feed, I keep the change gears at the lowest combination which is 20 80 20 80. I couldn't find anything on how to relate rpm and feed rate besides the table on the Mini Lathe User's Guide page 26 (littlemachineshop), and even then it doesn't tell you what tooth count is associated with 20 80 20 80.
I ran out of project time real fast, so I'm not sure when I'll be able to get another video up soon but you guys will be the first to know when I do for even more specific trouble shooting.
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