Page 5 of 9 FirstFirst ... 34567 ... LastLast
Results 41 to 50 of 90

Thread: Get me over the hump

  1. #41
    Join Date
    Jan 2004
    Location
    Missouri
    Posts
    30,054

    Default

    Quote Originally Posted by danlb View Post
    Too bad you haven't used a 7x10. Your very verbose post is based on false information. The 7xXX lathes have a "back gear" with a 1:2 reduction. I've turned 4 inch parts with no problems on a 7x10 and a 7x12.
    A 1:2 reduction is like nothing at all. doubles the torque and power applied, but multiplying anything by a small number does not get much.

    Unless the machine has a selection of belt or gear reductions, and I am pretty sure most are dependent on pure speed reduction for the bulk of the range, there will be a direct link of spindle speed and available power. You cannot dance around that, it is just physics, no matter how many words are used.

    So your statement apparently contending that the 7x machine is more powerful than a half HP SB is not true in real usage.

    Proof.....

    This Old Tony tried 20 thou DOC on a piece of 1 1/2" or so CRS at 80 RPM. The machine STALLED.... STOPPED. With a larger worpiece, that stall speed would be higher in proportion to diameter. But you would WANT the slower speed for larger pieces. HSS and a 4" piece would suggest 100 rpm, for a 100 SFM cut. Based on the video, you cannot do that cut.

    Might another machine be different? Sure. But the one Tony demonstrated has no backgear, it is 100% electronic speed control, and it behaves JUST AS I SAID.

    An SB, or Logan etc, will do that cut and more, EASILY, despite the "smaller" motor, and flat belts.

    What was that about bad information, again?

    https://www.youtube.com/watch?v=05vUCdzhoe4
    1601

    Keep eye on ball.
    Hashim Khan

  2. #42
    Join Date
    May 2015
    Location
    Somerset UK
    Posts
    1,836

    Default

    My 7x12 will stall drilling a 3/8 hole in steel, the PM you fancy is a much better bet, it has two speed ranges, up to 380 rpm in low and up to 2000 in high, giving reasonable torque in low.
    I recommend buying the Shars tool selection and some hss, either 1/2" blanks, or second hand, I'm with danlb on having tooling that definitely works and learning to make your own. There are books available on all aspects of getting to know how to use lathes, perhaps someone can recommend a good one.
    I wouldn't try more than a two thou depth of cut on my 7x12.
    Last edited by old mart; 01-10-2019 at 04:45 PM.

  3. #43
    Join Date
    Dec 2004
    Location
    East Coast, USA
    Posts
    7,381

    Default

    My 7x14 is OK. I've used it for about 15 minutes total. During that 15 minutes, it was just OK. I don't remember what I did with it, but I remember wishing to all hell that I had my bigger 13x40 lathe setup but at that time but I didn't even have 220v setup in my new shop yet so I was doing a few things with the 7x14.
    Work hard play hard

  4. #44
    Join Date
    Dec 2018
    Posts
    9

    Default

    Quote Originally Posted by JCByrd24 View Post
    In addition to danlb's comments, I'd note that many folks complain of the flimsy sheet metal stands supplied with a lathe, and the amount of vibration and resonance they allow. A rolling toolchest will no doubt be worse. I've battled chatter with my 1983 Enco 12" lathe with a change to 3 phase motor and VFD, replacing the compound with a solid block, and a lot of tuning including spindle bearing preload and it still finds resonance/chatter at higher RPMs at times. My next step is building either a dedicated concrete stand coupled to the floor, or filling the factory stands with concrete and bolting them to the floor and the lathe to them. The tops of my factory cabinets are small and at least 3/16" thick, but the whole system is just not heavy enough. I'd image a toolbox top will turn into a speaker.
    Hmm.. didn’t think about the tool chest resonating. I could wrap the exterior with sound deadening material used on cars. I can put it in every drawer as well. I plan to bolt the tool chest to the wall, shouldn’t be a problem. I also plan to machine/make leveling feel for the tool chest to get it off the wheels and be held in multiple spots instead of just 4
    Last edited by Lowlyslows; 01-10-2019 at 06:01 PM.

  5. #45
    Join Date
    Oct 2013
    Location
    USA MD 21030
    Posts
    4,790

    Default

    There are some important differences between AC induction motors and BLDC. Typically, an induction motor may have a peak torque of 2-4 times rated torque, and if not powered from a VFD or electronic overload device, it will achieve that torque before it stalls. A BLDC must be driven by an electronic controller, which will usually have overcurrent detection that may limit torque to much less than its maximum. I have searched some specs and it seems that typical BLDC motors have peak torque of about 3x, but I found one instance where peak torque was reported to be about 10x rated. That is usually found for series wound DC motors, but permanent magnet types are limited by the fixed field strength.

    https://electronics.stackexchange.co...d-stall-torque (0.56 Nm rated, 7.48 Nm stall)

    http://gemsmotor.com/12v-24v-48v-brushless-bldc-motor (1.0 Nm rated, 3.0 Nm stall)

    https://www.electrocraft.com/pdf.php...taSheet-US.pdf (about 3:1)

    https://www.edn.com/design/sensors/4...ing-Principles



    https://www.electrocraft.com/products/bldc/LRPX40/


  6. #46
    Join Date
    Jan 2004
    Location
    Missouri
    Posts
    30,054

    Default

    Bolting to the wall, if solidly done, should do more than almost any reasonable amount of sound deadening stuff. Any remaining noise, if annoying, may be attacked with the material.

    Make sure that the wall does not take over the resonance, though, it might be a better sounding board, or just send the noise throughout the rest of the structure, which is likely to make you unpopular with SWMBO. A concrete wall is probably safer that way than a stud wall that is attached to the floor above, etc.

    DO put something in the drawers to keep tools from rattling loudly.
    .

    .
    .

    Induction motor and torque.... Maximum usable torque is usually at about 80% of full speed, or a bit more (an overload condition, though). That is the "drop out" speed, where any more load slows the motor to a speed where it has less torque and will stall. Use of a VFD will modify that.

    The kicker is that an induction motor, or a BLDC or most any motor, is generally designed to work at full rated current indefinitely at the "base speed", which will be from half to max speed, likely more toward max. That gives best cooling. Higher torques take higher currents, and limit the time the motor can be run before overheating. While motors take a fairly long time to reach the peak temperature that the current flowing will cause (which in overload may be way too hot), they may exceed their rated max temperature much sooner as the amount of overload increases.

    Doubling the torque means doubling the current in a PM type motor,gives 4x the heating, and presumably reaches max allowable temperature 4x faster.

    With the little 7x lathes, and their electronic controllers, slowing the motor may also mean less cooling for the motor, so the overheating may occur even faster, assuming the controller actually allows any current over maximum for more than a very short time.

    The machines are probably basically very usable, and it would appear that the drive system is really limiting them to much less than their actual potential. I had a 1/3 HP motor on my little "109/AA/Craftsman 109.20630" lathe, which DID have back gear. The minilathes are considerably more robust than that "109" machine.
    Last edited by J Tiers; 01-10-2019 at 06:19 PM.
    1601

    Keep eye on ball.
    Hashim Khan

  7. #47
    Join Date
    Dec 2018
    Posts
    9

    Default

    SWMBO??

  8. #48

    Default

    She Who Must Be Obeyed ??

  9. #49
    Join Date
    Dec 2015
    Location
    Chilliwack, BC, Canada
    Posts
    4,612

    Default

    Looking at the manual for the PM 11x27 I see that again it's a variable speed with only two direct drive speed range options. So we're back to reduced speed means reduced watts of cutting power available. And typically at the very low speeds where you'll be wanting to carve metal off larger diameters that need high torque to push through the cuts. So I still put the Grizz G0602 higher up as a preferred "new lathe option" in this size category.

    Don't get me wrong. I love the idea of variable speed. But not at the cost of metal removing power. And the biggest thing I got out of This Old Tony's videos along with a few others I then watched on YT was the lack of power at reduced speed. And that same issue is going to haunt any lathe using a variable speed DC motor for the primary speed control. In fact if we look around You Tube at the mini lathe videos that's one big issue I see show up quite often.

    The mini and even these midi 9 and 10 inch size machines are solid enough that they SHOULD be able to handle more power. But it became pretty clear to me that the variable speed is the kiss of death to using them well. And that's why I've said that the old South Bend with the "whimpy" 1/2hp motor running through the full power speed and torque conversion of the belts and pulleys in the drive setup is a far better option. In fact a geared via pulleys setup attached to the 7x mini lathes would likely be a huge upgrade. The lathe itself is easily sturdy enough to handle the extra torque such a drive would provide.

    But again this isn't a modification that a new owner should be facing. Thus why I'm suggesting some other options.

  10. #50
    Join Date
    Dec 2018
    Posts
    9

    Default

    Quote Originally Posted by Ringo View Post
    She Who Must Be Obeyed ??
    Pffft.. I run this house!!��

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •