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Thread: Get me over the hump

  1. #61
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    I honestly don't think toolgrinding should be difficult. But it takes 2 things.. which a lot of people don't have..
    You have to apply yourself and make a real effort.
    2nd clearance, clearance , clearance.. that is how it works.. the edge doing the cutting has to touch first and be sharp.. everything else needs clearance., and rake, you have to understand rake, so you don't get too much clearance..
    It's easy once you understand clearance. .

    But you learned to TIG weld so I think, you will find it easy..

  2. #62
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    Quote Originally Posted by Lowlyslows View Post
    Trying to follow you guys here and please excuse my ignorance. Is the PM 1127 lathe going to be weak at lower RPMs with the 1.5hp motor?
    We do not know without a closer look.

    The manual is at http://www.precisionmatthews.com/wp-...anual-2015.pdf

    According to that, the speed changing is in two ranges (page 16) which are 50 to 850 rpm, and 110 to 1800 rpm. This is not ideal.

    Assuming, as is reasonable, that the 1800 speed (or 850) represents the motor running at design speed and rated power potential, that is the 1.5 HP point. then, at 50 rpm, the power available at the spindle would be 64W, or about 0.08 HP. That is one heck of a drop in available power.

    Even if the actual motor base speed were at 900 (or 425) spindle rpm, the spindle power would still be 0.16 HP, far far less than the advertised 1.5 HP motor should be capable of. The machine is probably perfectly fine for smaller diameter work, bit if you ever really do need the low 50 rpm due to a klarge workpiece, you will most likely find that you are limited to tiny cuts, taking a long time to do what a Southbend or other machine (that has a back gear and belts) would breeze through.

    Maybe that is no problem to you, I cannot tell you that, you must tell us that. But it is evidently a lathe that will struggle with slower speeds and larger work, unless you make modifications.

    It appears that the machine is made to show good specs for whatever the makers believe is "the usual sort of work", while pushing the problems off on the things they think you will seldom want to do, and can therefor tolerate hassles with.


    If the makers of the PM machine had chosen a different set of ranges, that did not overlap so much, they would have avoided that issue. For instance, if they had set it up for 350 to 1800 and 70 to 350, then the ranges would not overlap, anf the worst power output would be abut 1/4 HP, not great, but better.

    With 3 ranges, they could have had it all....variable speed over the full range of speeds, with a range of 50 to 165, then 165 to 550, then 550 to 1800. The worst power would be 1/2 HP at the low end of each range. But the drive would be more complex, and the cost higher.

    It also looks from the table on page 27 that if you want to cut threads, you will be doing a lot of gear changing, although the machine will cut metric or inch threads when set up right.

    Per danlb's comment.... if you assume using 3x speed for carbide, then that is 150 rpm, and just about 1/4 HP at that speed. Still not very good, not even equal to my little Logan with it's 1/3 HP motor.

    I do not know that I personally would want to have this machine.
    Last edited by J Tiers; 01-10-2019 at 10:32 PM.
    1601

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  3. #63
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    Quote Originally Posted by jmm03 View Post
    not to derail this thread, but what is an outdoor sock drier???
    Mr. Socktopus

  4. #64
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    Let's look at the numbers for the 11x27 PM lathe and make a few comparisons to fixed speed motor lathes with gearing.

    The manual says it has a 1.5hp motor that runs at max 4600 RPM. in the low 50 to 850 speed range the motor to spindle ratio is 4600/850= 5.4. So actually better than 4:1.

    Now I did find an "induction head" in the wiring diagram so it looks like it may try to push more power into the motor to hold the set speed.

    But the motor will be limited in how much current can be fed to it before it overheats. If it's limited to the full speed current it will only produce 1/8.5 of max HP or 0.18HP. If it feeds more current to the motor when loaded down then it can make up for some of the loss due to the low RPM. Double the full power current would still only up the HP to 0.36 at that speed.

    It's one of those things where I'd want to try before I were to buy or talk with someone that has that actual lathe and find out what it will bull it's way through at low RPM. IF there's been some significant work put into how the motor is driven and how the wall power is converted to drive the motor it might work well. But when was the last time we saw Asian products made to a lower price point put that much work into something?

    OK. let's look at a South Bend 9 running a 1/2HP motor 1725rpm motor at the same 100 RPM spindle speed. Right off the bat the gear ratio is easy at 1725/100= 17.25. So about 3 times lower geared than the PM lathe to bull through cuts at 100 RPM.

    Yes, a lot of the use for low RPM is to allow getting the SFM low enough for HSS tooling. And carbide cutters can easily tolerate much higher cutting speeds. They love it actually. But removing that much more metal REALLY bogs down the machines and flexes the beds. And one can quickly find out just how chatter prone they are as a result. Plus a lot of shapes can't be easily found in carbide and it's handy to have some HSS around for them. And then you're back to needing good performance at low RPM.

    All in all I still look at the torque multiplying pulley arrangement on that Grizzly G0602 machine and I think it's a safer bet.

    Geoff, I gotta agree with Mcgyver. That's a nice setup. I suspect the MDF laid down for the lathe to sit on greatly aided with soaking up some flex. It gives me the idea that similarly dropping the cabinet down so it's directly on the floor like you did then using something like a length of Paralam beam as the base for the lathe would be a very nice added rigidity setup. It's got the storage so much needed and it would see the machine bolted down to the stable and stiff wood beam that bridges over any sheet metal flexing of the cabinet.

    Lowlyslows, sorry to complicate this thread with all the techy talk. But I think it's important to you to understand the options and side effects. Especially if some day you want to put a large brake drum off some old car into your new toy and skim off the working faces. On small items you'd never notice.
    Last edited by BCRider; 01-10-2019 at 11:07 PM.

  5. #65
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    I remember cutting .062 depth of cut with HSS on a Southbend.. 1/8 material coming off..
    To rough out certain piece would take huge amount a of time if you can only cut half of that.

  6. #66
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    Ya know... The variable speed thing may not be without some issues. But I was just catching up with Brian's engine making thread and it occurs to me that he's running a variable speed lathe and I'm pretty sure it's the Busy Bee CX706 10x22. It would be interesting to see what his thoughts on this variable speed thing are for a lathe. I may be making more of a case against it than it deserves.

  7. #67
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    Quote Originally Posted by BCRider View Post
    Ya know... The variable speed thing may not be without some issues. But I was just catching up with Brian's engine making thread and it occurs to me that he's running a variable speed lathe and I'm pretty sure it's the Busy Bee CX706 10x22. It would be interesting to see what his thoughts on this variable speed thing are for a lathe. I may be making more of a case against it than it deserves.
    You are not telling any fibs.

    The question is always whether any particular person's work is affected by the issues you (and I) brought up. If your biggest piece is 2 or 3" diameter, there may be no issue. If you do larger parts, or if you need large DOC, there may be an issue.

    The little Logan I have will happily turn material up to the full diameter that will swing on the faceplate. I have done work several times that was within an eighth of an inch of hitting the ways, and found no issues. That would have been somewhat over 10" diameter, since the Logan is nominally 10", but swings about 10 3/8 or so. I did large (vs the swing) work on the tiny "AA/109" also.

    But others may never need that and have no troubles with a machine that struggles with large diameters. Probably the largest things that Brian Rupnow turns are the flywheels, up to maybe 6" as I recall. Large enough to be potentially an issue when roughing fown, but he'd be the one to ask.

    Asian machines often have not had back gears, and now they have gone to having mostly "knob variable" speed on the spindle for many, as well as "partial quick change" gearing that gives 3 related thread settings per manual change gear setup.

    Obviously they think, perhaps correctly, that people rarely turn large stuff, and do not thread things single point very often. If that is a correct assessment, then the makers made the right choice.
    1601

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  8. #68
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    I have two lathes - 7x20 and 11x42. I have a 1972 MGB.

    I hardly ever use the smaller lathe. This Old Tony recently had a video in which he talked about tuning up one of those little LSO's (lathe shaped object) and he was able to get it to a useable condition by bolting it to a THICK welding table, replacing the bearings, etc. I might try that and hope that I can tune it up so that it will be useful for parts smaller than my thumb. Until then the old Delta-Rockwell 11x42 is my "go to" lathe for almost everything.

    I use the lathe to make some parts for the MGB... bushings, little gizmos, plugs for the vacuum manifold, a replacement for a seat bracket bolt, etc. However, over 2 million MGB's were imported into the USA over 25 years and so there are not only parts available from wreckers, there are companies who do a brisk business in selling new and new-old stock parts. So I don't need to use my machine shop to make parts very often.

    A friend has an early 1950's Jaguar. He doesn't have the same luxury. He has made a lot of replacement parts including suspension parts and a piston head. I don't think he could keep that thing running without a lathe, mill, etc.

    However... truth be told... while I fell in love with old cars before machining and used the cars as a partial excuse to buy the machines, at this point I'd rather give up my old car than my machine tools.

  9. #69
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    Quote Originally Posted by Ringo View Post
    Look at this in the $3000 price range:
    https://www.theequipmenthub.com/used...-engine-lathe/
    While BIG is good there is often a limit how big you want (again, ask your wife)

    -4000 lbs weight can be issue in some cases
    -only 1200 rpm top speed, I'd really want 2000 rpm for "general purpose" medium size lathe
    -chuck of that size is something like 80lbs, not that fun when you need to change the chuck. Less issue if you work with 200lbs shafts and already have shop crane over lathe.

  10. #70
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    Quote Originally Posted by BCRider View Post
    Ya know... The variable speed thing may not be without some issues. But I was just catching up with Brian's engine making thread and it occurs to me that he's running a variable speed lathe and I'm pretty sure it's the Busy Bee CX706 10x22. It would be interesting to see what his thoughts on this variable speed thing are for a lathe. I may be making more of a case against it than it deserves.
    that depends.....facts are facts, how much they matter is an individual thing. Nevertheless, if you expect close to same the performance from an electronic speed control vs mechanical, you better go up in a power a few magnitudes of motor power. Its likely true for most that there's some standard distribution of work size vs possibly work envelope of the machine so some will say this doesn't matter for what I do. Fair enough for them, for me I look at as you never know what work you'd be called upon to do and the trick is often pushing the envelope so maximum capabilities are best and some times you want low speed (i.e. tapping) other than for large diameters.

    I've VFD's and DC controllers on several machines and like them a lot, but in all cases the original mechanical reduction is still there or even enhanced (two stage belt drive)
    Last edited by Mcgyver; 01-11-2019 at 09:24 AM.
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