Tips on machining pulley grooves
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As part of my 24v re-motoring exercise I¡¯m making new pulleys from aluminium. I¡¯m not finding it easy to machine the groove for the belt and would appreciate any tips (apart from ¡®buy them online¡¯ and ¡®do it on a bigger lathe¡¯ - I just have the U3).
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Use a hacksaw blade to remove some of the material before you use your tool, and that might help. Might also be "Interesting" trying to get just the right depth... ;) perhaps used a hacksaw blade, or piece of hacksaw blade, as a parting tool before cutting to depth with your profile cutter.? Bill in OKC William R. Meyers, MSgt, USAF(Ret.) Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY! Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first.
On Saturday, September 16, 2023 at 03:12:26 PM CDT, Peter Brooks <peter@...> wrote:
As part of my 24v re-motoring exercise I¡¯m making new pulleys from aluminium. I¡¯m not finding it easy to machine the groove for the belt and would appreciate any tips (apart from ¡®buy them online¡¯ and ¡®do it on a bigger lathe¡¯ - I just have the U3).
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All of what you say can be improvements.? The root problem is a lot of cutting surface all at once on a large diameter in a small minimally powered machine. Going in at two different X positions as you mentioned will help to mitigate this.? And, also, to an extent the chip formations from the left and right sides of the tool will, to some extent, both try to move into the same airspace above the tool bit.? They effectively collide there making things worse.? (The is the reason why single point thread cutting is ideally done at a 29 of 29.5 degree angle so most cutting is only on one edge.? Because for thread cutting this collision of the "left" and "right" chip can be severe.) You also mentioned what accounts to first roughing the shape.? This can be done with a narrow square end tool (such as a cut off tool because it takes a lot of grinding to make a narrow tool from a standard size tool bit) to make a number of cuts resulting in a stair step shape to approximate the final.? You still have the issue of a large diameter in a too small machine.? But will have the advantage of having a much smaller cross section of the cut.? Then finish with the forming tool.? Or it might even be possible to use a round file that is, or has a region that is, the correct diameter. Beyond that, it is important to have really sharp tool bits, a slow speed, and a lot of patience.? A cutting fluid for aluminum might help.? But with minimal removal rates, it might not make much difference.? And you probably aren't going to be able to get the part so hot that you have to worry about tool bit temperature.? But you never now. This is also an example where just because something fits the envelope of a machine, it is not necessarily comfortably within the machine's capability.? There are parts that might need a large swing to clear, but a small diameter is actually being worked on such as boring a hole or machining a smaller diameter feature.? That's different. Sometimes the easiest solution is to use a larger machine to make the part.? And if you don't have one, find somebody who does. Charles E. "Chuck" Kinzer
On Saturday, September 16, 2023 at 01:12:27 PM PDT, Peter Brooks <peter@...> wrote:
As part of my 24v re-motoring exercise I¡¯m making new pulleys from aluminium. I¡¯m not finding it easy to machine the groove for the belt and would appreciate any tips (apart from ¡®buy them online¡¯ and ¡®do it on a bigger lathe¡¯ - I just have the U3).
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¿ªÔÆÌåÓýHello
Peter: You are right, taking cuts from different angles will help a lot. Just because a big lathe could form cut this pulley in one plunge, doesn't mean you must. Lots of lighter cuts are OK. Just to let you know the risk of pushing your motor to the limit, I pushed my Smithy Granite to mill a welded channel square. Then there was this funny smell and a bit of smoke came out of the motor! It isn't dead yet, but I need to plan on a new motor soon. I'm thinking 3 phase with a variable frequency drive (VFD) so I can have full torque at lower speeds. Carl. On 9/16/2023 5:20 PM, Peter Brooks
wrote:
Thanks both, good advice and sounds like a mix of steps would be the way forward. Roughing out, followed by left / right cuts before a final, slightly deeper forming cut. |
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Oh, so very well done! Congratulations! Bill in OKC William R. Meyers, MSgt, USAF(Ret.) Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY! Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first.
On Saturday, September 16, 2023 at 04:28:48 PM CDT, Julius Henry Marx <sawbona@...> wrote:
Hello: On Sat, Sep 16, 2023 at 06:20 PM, Peter Brooks wrote: ... the U3 probably isn¡¯t quite up to the task.There's a more than one way to skin a cat, just that sometimes you have to push the envelope a bit more than would otherwise be comfortable. I was in the exact same spot, did not want to spend absurd money on something I was (reasonably) sure I could make myself but only had my Unimat 3 to work with. Check [url=https://www.model-engineer.co.uk/forums/postings.asp?th=187100]this[/url]thread at ME. Best, JHM |
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I took a machine shop class in high school, finished the class and graduated from high school right around 50 years ago. A bit over 15 years ago, I bought my first lathe. One of the Chinese Mini-lathes, a Harbor Freight 7x10, model 93212. That was around August 2008, IIRC. From then until December of 2014 I had the devil's own time trying to get that lathe to do what I wanted it to do. Got a lot of great help from this and other boards over at Yahoo groups, before they crashed and burned. Still wasn't doing all that good with my life. My wife got tired of my griping about it, and told me to take another class! So I did. Started in February 2015, and I finally completed it in May of 2022. That's 7 years and 3 month, to the day. It was supposed to be an 8 or 9 month class if you attended full time. And I started full time, but was also working full time, and I'm not a teenager anymore. ;) I think I made it through the first couple of months, but after that, it was two nights a week, 3 hours per night. One of the things I learned in that class was that I had completely forgotten (assuming I had ever learned) how to measure parts accurately. The class taught me that, and a bit of practice with their equipment, including a set of Johannsen blocks to practice on, fixed that in a couple of days. I searched messages for your first questions here. And that was not a whole lot over a year ago. It took me 7 years to figure out I was failing abjectly, and 7 more to do a lot better. I should be a better machinist than you are. But I would be willing to make a small wager that if I am, it won't be for long! You've made tremendous progress in just over a year! I'd have to be blind and stupid to not recognize that! I will admit to being crazy, but I try not to be stupid! ;) Oh, and there wasn't a single thing wrong with my first lathe that a bit of skill wouldn't have been able to overcome. All the problems were the "Stick Actuator" as we Air Force folks call it. :) Bill in OKC William R. Meyers, MSgt, USAF(Ret.) Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY! Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first.
On Saturday, September 16, 2023 at 05:54:06 PM CDT, Julius Henry Marx <sawbona@...> wrote:
Hello Bill: On Sat, Sep 16, 2023 at 07:19 PM, Bill in OKC too wrote: ... well done! Congratulations!Thank you, appreciate your saying so. 8^) Best, JHM |
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The formula we used at school is rpm=SPM/d*4.? For aluminum, SPM is 400-1000 from a chart, 38mm is 1.5" approximately, and back in the day it was ¦Ð or 3.14159 or however many decimals you cared to carry it out. 4 is easier and still close enough for practical purposes.? I got 1066rpm, but 1000 or 1100 should be fine, too. That's with high speed steel tooling. Also on an industrial lathe. They need to worry about how many parts they can produce in a day, where a hobbyist usually doesn't. If you use carbide tooling on a big machine, you can cut about 4x faster, but you are working on a U3, so forget about that! :) Lathes have speeds determined by the gears or pulleys used to reduce the motor speed, and my experience is that very few have continuously variable speed, so you use the closest setting you can to your calculated speed.? Unless it doesn't work. Then you try the next step. Up or down, and try it, and see, feel, and heat. If it's better, carry on, and if not try a different speed! To eliminate chatter, slower is usually better,? ut not always. Sometimes you'll need to speed up, sometimes down, and only trying it will tell you which is better. If it's chattering like mad, try a different speed. On large stock, and as you get deeper into it, you may need to change the speed several times, since your effective diameter changes.? Some pretty fancy machines will continuously vary the speed for you. Good luck finding one like that! I've read about them, but never seen one. ;) HTH! Bill in OKC? William R. Meyers, MSgt, USAF(Ret.) Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY! Physics doesn't care about your schedule. The only reason I know anything is because I've done it wrong enough times to START to know better. Expect in one hand, expectorate in the other. See which one gets full first.
On Sunday, September 17, 2023 at 01:46:43 AM CDT, Peter Brooks <peter@...> wrote:
Bill, thanks for your kind words. I¡¯m sure you are doing far better than you think you are! ?Life long learning eh?? JHM, thanks for the link to the ME post. |
¿ªÔÆÌåÓýHi
Bill: You are right, fancy machines, usually those with CNC, change speed with diameter. It can be part of the program. And in production, time matters. The valve seat we were grinding, they allowed 10 seconds to finish the job. The best lathe I've ever run is a Hardinge HVL toolroom lathe. The head stock was driven by a continuously variable belt drive. And the carriage feeds were driven by DC motor with a variable power supply. If something chattered, just twist one of the knobs until it cut right! Don't get me started about threading, it was a total cheat on a Hardinge. For speeds I just remember 1000 RPM for a 1/4" drill in steel. Double and Half from there: Double diameter and Half speed: 500 RPM for 1/2", etc. Faster for aluminum and plastic, until it melts. Carl. On 9/17/2023 8:28 AM, Bill in OKC too
via groups.io wrote:
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¿ªÔÆÌåÓýFor
Computers I thought it was the "Keyboard / Chair Interface
Unit" cause all the problems. On 9/17/2023 5:50 AM, Peter Brooks
wrote:
On Sun, Sep 17, 2023 at 12:18 AM, Bill in OKC too wrote: |
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Do you have the compound/taper attachment for your U3? If so there is a very easy way to cut a V.
Using a parting tool cut into the pulley to the depth required. Then set the compound to feed into the workpiece at half the required angle say 20 degrees. Then just turn the internal corners with the parting tool until they meet the bottom of the V. This is how I do it on my Cowells lathe. Easy. ? |
Bill in OKC too
Carl
Unimat Matt