Beer, huh? I've heard of using dry ice in an alcohol bath to cool parts for a shrink fit, but never thought of trying that with beer.
Oh, wait - you were drinking the beer? Never mind, carry on ...
Cx701 lathe report
- Thread starter Brian Rupnow
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Beer, huh? I've heard of using dry ice in an alcohol bath to cool parts for a shrink fit, but never thought of trying that with beer.
Oh, wait - you were drinking the beer? Never mind, carry on ...
Found it - in a biscuit tin full of boiler burner spares... Another project I am doing while I was awaiting the brushes.
Should have gone for a beer, then I would have found it later!
K2
Should have gone for a beer, then I would have found it later!
K2
On more than one occasion I have managed to ‘lose’ the micrometer without taking one step away from the lathe.
I slept well last night. Today I'll make some more no 8 jets (0.25mm diameter jet), a couple of venturis, and maybe ceramic burner or 2. I need to sell 1 a month to have a"kitty" for tools, after costs. If I need a new Variable Speed Board for the lathe it's a tidy £130... so I need to sell a lot of burners!
I read about the use of PM Brush motors with speed control (DC), compared to field coil types of universal motor (AC). Ill be checking today, but I think mine is a DC PM Motor. But there has also been discussion between single phase AC and 3 phase AC - with variable speed.
However, to suit me, I should like to understand the advantages/differences between comparable 3-phase variable speed and DC PM with variable speed. Does the 3-phase variable speed have higher or lower torque at low speed? Does the 3-phase variable speed have a wider speed range than the DC PM Motor - that seems to be limited by Brush "flash-over" - or some switching that is causing high voltage spikes? Not understanding these things tells me not to change - but if the variable speed unit decides to loose all the "electronic internal smoke" I shall have a large bill - or need to find an alternative?
What do you guys know? - I suspect the lathe is built with a compromise to get what it does with the cheapest option...
Ta,
K2
I read about the use of PM Brush motors with speed control (DC), compared to field coil types of universal motor (AC). Ill be checking today, but I think mine is a DC PM Motor. But there has also been discussion between single phase AC and 3 phase AC - with variable speed.
However, to suit me, I should like to understand the advantages/differences between comparable 3-phase variable speed and DC PM with variable speed. Does the 3-phase variable speed have higher or lower torque at low speed? Does the 3-phase variable speed have a wider speed range than the DC PM Motor - that seems to be limited by Brush "flash-over" - or some switching that is causing high voltage spikes? Not understanding these things tells me not to change - but if the variable speed unit decides to loose all the "electronic internal smoke" I shall have a large bill - or need to find an alternative?
What do you guys know? - I suspect the lathe is built with a compromise to get what it does with the cheapest option...
Ta,
K2
goldstar31
Well-Known Member
Goodmorning Ken.
The question seems to hinge on the Sale of Goods Acts of what is 'merchantable quality' and how longer a guarantee/warrantee was implied when you bought your lathe. I'm not 'shot gunning\ overall but precisely what the terms were on the electrical parts.
As I reported earlier, my Sieg circuit board for the vertical mill column milling attachment failed quicker than immediately.
No doubt a question to the seller of the new lathe would go a long way to clarfy the issue.
Best Wishes
Norman
The question seems to hinge on the Sale of Goods Acts of what is 'merchantable quality' and how longer a guarantee/warrantee was implied when you bought your lathe. I'm not 'shot gunning\ overall but precisely what the terms were on the electrical parts.
As I reported earlier, my Sieg circuit board for the vertical mill column milling attachment failed quicker than immediately.
No doubt a question to the seller of the new lathe would go a long way to clarfy the issue.
Best Wishes
Norman
The helpful guy at Chester Machine tools had explained to me what the Variable Speed board does so I can check it and see if I'm trying to send too many volts to the motor... and adjust the pot if necessary. If I get it wrong - "It has been good corresponding with you all" - as I shall be the charred looking thing next to the lathe! - I'll wear my wellies and rubber gloves!
K2
K2
Just to complicate things - in addition to AC motors and permanent magnet brushed DC motors, there are also brushless DC motors which require a special control board. As I understand it - which is not very much! - these are somewhat analogous to a 3-phase motor on a VFD. I have now completed the entire information dump of everything I know ...
BaronJ
Grumpy Old Git.
Hi Ken,
To answer your questions you need to understand that both single and three phase induction motors speed is a function of the voltage supply frequency and the number of poles.
All induction motors are rated at a specific supply frequency. Within a quite small tolerance band the output power and hence torque will be at the rated figure. As the frequency moves away from the specified supply value the power output falls off.
In the case of three phase speed control the output power falls of more rapidly as the frequency is reduced and the motor gets slower. Some VFD compensate for this by raising the voltage supplied to the motor. The downside of this is without additional cooling the motor can overheat and fail. Normally you wouldn't run the motor at 25 Hz for any length of time, nor would you want to run the motor at 125 Hz for any length of time either.
So the answer to your second question is yes the DC variable speed motor does have a much greater speed and power range than and equivalent power three phase motor.
A DC motors speed is a function of the amount of voltage that is supplied to it, irrespective of whether it uses field coils or a permanent magnet. The use of a PM field has the advantage of cost and physical size, resulting in a smaller frame for the power rating. Again the downside is heat ! The only way the heat can escape from a PM motor is by conduction through the bearings and forced air through the motor. So PM motors tend to run hotter than the equivalent AC motor.
To answer your questions you need to understand that both single and three phase induction motors speed is a function of the voltage supply frequency and the number of poles.
All induction motors are rated at a specific supply frequency. Within a quite small tolerance band the output power and hence torque will be at the rated figure. As the frequency moves away from the specified supply value the power output falls off.
In the case of three phase speed control the output power falls of more rapidly as the frequency is reduced and the motor gets slower. Some VFD compensate for this by raising the voltage supplied to the motor. The downside of this is without additional cooling the motor can overheat and fail. Normally you wouldn't run the motor at 25 Hz for any length of time, nor would you want to run the motor at 125 Hz for any length of time either.
So the answer to your second question is yes the DC variable speed motor does have a much greater speed and power range than and equivalent power three phase motor.
A DC motors speed is a function of the amount of voltage that is supplied to it, irrespective of whether it uses field coils or a permanent magnet. The use of a PM field has the advantage of cost and physical size, resulting in a smaller frame for the power rating. Again the downside is heat ! The only way the heat can escape from a PM motor is by conduction through the bearings and forced air through the motor. So PM motors tend to run hotter than the equivalent AC motor.
BaronJ
Grumpy Old Git.
Hi Andy,
Yes, you are right ! BLDC motors are fundamentally three or more phase machines and do require a special controller.
A BLDC motor could have as many as twelve phases depending upon the duty that it has been designed for. The controller is as you suggest akin to a VFD as it can offer variable motor speed control.
These motors and the controllers can be found on just about every hard disc drive made in the past 20 years or so. Primarily used because the rotational speed can be very precisely controlled often using a quartz crystal.
Yes, you are right ! BLDC motors are fundamentally three or more phase machines and do require a special controller.
A BLDC motor could have as many as twelve phases depending upon the duty that it has been designed for. The controller is as you suggest akin to a VFD as it can offer variable motor speed control.
These motors and the controllers can be found on just about every hard disc drive made in the past 20 years or so. Primarily used because the rotational speed can be very precisely controlled often using a quartz crystal.
See, I knew that I knew enough to be dangerous!
I have seen BLDC motors starting to show up on some smaller machines where a permanent magnet brushed DC motor might have been in the past. I'm guessing the extra complexity of the controller is no longer much of an issue - maybe there is a single-chip solution that takes care of it.
Actually ... I have a fuzzy memory ... are tiny BLDC's often used in drones?
I have seen BLDC motors starting to show up on some smaller machines where a permanent magnet brushed DC motor might have been in the past. I'm guessing the extra complexity of the controller is no longer much of an issue - maybe there is a single-chip solution that takes care of it.
Actually ... I have a fuzzy memory ... are tiny BLDC's often used in drones?
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How about a description of the belt? I found a perfect replacment for my unimat sl belts at Horrid Fright disguised as a $5 belt for a rock tumbler! Bill in Boulder CO USA
