Brush Or Brushless Motor For A Mini/midi Lathe?

If low speed torque matters to you, in general brushless DC (BLDC) motors have more torque at low speeds than their brushed counterparts. That's why brushed mini machines have hi-lo gear shifts or multi-sheaved pulleys with a set number of speeds available, like the Jet 920. That's to keep the motor up on its torque curve at low spindle rpm. BLDC belt drives, like the LMS, run min to max RPM (motor and spindle) with no gear/pulley shifting. I don't know how the PMs are set up. If you do most of your work at a single speed, it's no big deal one way or the other. Some may say no big deal, period. All 3 of the machines you listed require messing with change gears to do threading.

That said, I had a 7x14 that had no trouble threading at 60-70 rpm in low gear. I now have an LMS 8.5x20. I have turned and faced a 4" aluminum "hockey puck" on it, but most of my work has been turning and threading aluminum, mild steel and brass up to 3/4" round. That is about the largest size that will fit through the spindle. (actually something like 20mm if I recall). It's a very well made machine, as I'm sure the others are, too. A lot of folks on the forum also speak highly of the PM machines.

Tom
 
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i would take the mathews just to have the bigger bore
 
Thank you all again. It looks like both machines will serve my needs. I am surprise few talk about the Jet 920.
 
The Jet 920 design has been around for a long time, but is a very basic lathe for the price. Even with the "discount" I do not think it is a wise purchase for the price. With the newer designs, variable speed, larger spindle, less gear changes, more feeds and thread options, etc..., there are better options these days in this size and price range. The other factor is the total package, options and support after the purchase. Many of these smaller lathes work but are very minimal in design and features. If you are spending 2-3K for a lathe, I feel there are a lot better options. Either the PM127 VF-LF or the PM1128, would offer a lot more range features and an flexibility whether you do small or larger work. Many of the newer smaller lathes with variable speed use a DC motor, usually brushless. Given there size, they have more than adequate power running them off of 120V, and should do anything you want them to do. If you want smaller, then maybe look at something like the Grizzly G0752 - 10" x 22" Variable-Speed Lathe. http://www.grizzly.com/products/10-x-22-Variable-Speed-Lathe/G0752
 
I live in a small Quaker founded town just across the river from Philadelphia, many wealthy business owners built large summer homes along the riverbank, to this day it is a dry town, one can not sell a glass of wine with dinner at a
TonyL said:
This is why I ask:

http://littlemachineshop.com/products/product_view.php?ProductID=3540&category=1271799306

Can I expect to have problems with a brushless variable speed motor?

Versus this:

http://precisionmatthews.com/PM1027Lathe.html
Click to expand...
Yes, one can expect problems from any system that makes a dedicated effort at being the lowest cost alternative, however I suspect that if you bang on the vendor to keep sending you new products every week you will end up with something that works for you.
Your mileage may vary, I am in no way disparaging any company linked above, I merely work in a jobshop 50 hours per week, that is more then enough machine work for me.
 
Thanks again folks. It looks like I have beaten this subject to death. I do continue to look for an "old" non-overseas lathe, but I haven't seen any that I am equipped to fix/appraise its needs. Your guidance and experience is very much appreciated and highly respected.
 
Given I want to turn SS (304L, 303, 316): Is there a big difference between a 1 HP brushed motor, and a 1.36 HP brushless motor? Would I benefit from 33% more HP? Is HP simply HP, regardless of brushed or brushless?

Thank you!
 
Short answer, most likely no, especially because you previously mentioned doing small diameter turning. It is unlikely you will see a difference, and even if you could, you could take a slightly smaller cut. It also depends on the belting or gear ratio. Brrushless motors are about 10% more efficient then a brushed motor.

A DC Brushless Motor uses a permanent magnet external rotor, three phases of driving coils, one or more Hall effect devices to sense the position of the rotor, and the associated drive electronics. The coils are activated, one phase after the other, by the drive electronics as cued by the signals from the Hall effect sensors, they act as three-phase synchronous motors containing their own variable frequency drive electronics.

BLDC Motor Pros:
Electronic commutation based on Hall position sensors
Less required maintenance due to absence of brushes
Speed/Torque- flat, enables operation at all speeds with rated load
High efficiency, no voltage drop across brushes
High output power/frame size.
Reduced size due to superior thermal characteristics. Because BLDC has the windings on the stator, which is connected to the case, the heat dissipation is better
Higher speed range - no mechanical limitation imposed by brushes/commutator
Low electric noise generation

BLDC Motor Cons:
Higher cost of construction
Control is complex and expensive
Electric Controller is required to keep the motor running. It offers double the price of the motor.

A Brushed Motor has a rotating set of wound wire coils called an armature which acts as an electromagnet with two poles. A mechanical rotary switch called a commutator reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor. As the poles of the armature electromagnet pass the poles of the permanent magnets, the commutator reverses the polarity of the armature electromagnet. During the instant of switching polarity, inertia keeps the classical motor going in the proper direction.

Brushed Motor Pros:
Two wire control
Replaceable brushes for extended life
Low cost of construction
Simple and inexpensive control
No controller is required for fixed speeds
Operates in extreme environments due to lack of electronics

Brushed Motor Cons:
Periodic maintenance is required
Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque
Poor heat dissipation due to internal rotor construction
Higher rotor inertia which limits the dynamic characteristics
Lower speed range due to mechanical limitations on the brushes
Brush Arcing will generate noise causing EMI
 
Amazing! Thank you. I am looking forward to the when I can pay-it-forward with my knowledge. I got a feeling it is a long way off. Thanks again.
 
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