[jmille25]

About ready to pull the trigger and order servos and drives from DMM, but want some reassurance from others. I was originally planning on using their 750W servos, but after talking to a member of their tech support, he recommended the 400W servos. Before I spend a non-zero amount of time making adapter plates and bushings...do the 400W servos sound reasonable? So far DMM has been extremely helpful and their customer service top notch, I just really don't want make things twice...

The BTC has 2:1 reductions on XYZ. Info on the current DC servos...

Kt 1.68 in-lb/amp
Ke 19.8V/1000rpm
Jm 0.0092 in-lb/sec^2
Amp cont. 6.3
Amp peak 58
RPM 4000 max

Any help would be greatly appreciated,
Josh

[mactec54]

About ready to pull the trigger and order servos and drives from DMM, but want some reassurance from others. I was originally planning on using their 750W servos, but after talking to a member of their tech support, he recommended the 400W servos. Before I spend a non-zero amount of time making adapter plates and bushings...do the 400W servos sound reasonable? So far DMM has been extremely helpful and their customer service top notch, I just really don't want make things twice...

The BTC has 2:1 reductions on XYZ. Info on the current DC servos...

Kt 1.68 in-lb/amp
Ke 19.8V/1000rpm
Jm 0.0092 in-lb/sec^2
Amp cont. 6.3
Amp peak 58
RPM 4000 max

Any help would be greatly appreciated,
Josh

The original DC servos were quite wimpy, in terms of performance, as were lots of retrofit kits for them, so if they calculated using those old motor spec's then that is why they came up with the 400w motors which would not be a good outcome

The 400w will do the job at 2.1, but I would not recommend to use the 400w, I have done some of these machines and found that 750w is a good fit, if you are serious about machining

You could use 400w on your Z axes, but use 750w on the X and Y axes, in reality 750w is the choice for all axes, and the Dyna4 drives to get the max RPM, Dyna 2 Drives if you are not concerned about speed although the new Dyna 2 Drives you can run at 72v which helps to get the RPM up higher

[jmille25]

mactec, thanks for the information! I'm feeling much more at ease about this purchase.

Side question...down the road I have thought about adding a servo to power the knee. Right now there is a 2:1 reduction between the crank and the ballscrew...do you think the 750W servo would have enough 'oomph' with a 4:1 reduction or would the 1kW servo be a better choice?

Regards,
Josh

[G59]

750W = 1 hp.
400W = a little more than 1/2 hp.

[mactec54]

mactec, thanks for the information! I'm feeling much more at ease about this purchase.

Side question...down the road I have thought about adding a servo to power the knee. Right now there is a 2:1 reduction between the crank and the ballscrew...do you think the 750W servo would have enough 'oomph' with a 4:1 reduction or would the 1kW servo be a better choice?

Regards,
Josh

You want to power the Knee just for positioning, then the ratio could be whatever you needed to make it work, most use more than 4:1 for this, a photo of your machine would be good,are you sure you have a Ballscrew on the Knee Jack, most just had a acme screw thread

[2ndSteel]

You want to power the Knee just for positioning, then the ratio could be whatever you needed to make it work, most use more than 4:1 for this, a photo of your machine would be good,are you sure you have a Ballscrew on the Knee Jack, most just had a acme screw thread

I have recently replaced the DC servos on my Enco BP clone with DMM 750W ac servos. I used the same mounts and 2:1 bet drive on the X and Y. I use a 750W on my Z which is the knee. This has a 5:1 planetary gear drive with a 1:1 belt. I am still woking with motor tuning but have 120ipm on X and Y and 80 on the Z. The most I could get with the DC drives was 60ipm and 45 so I am quite pleased so far. Still have to get the spindle hooked up and do some cutting. Somany projects, so little time.

[jmille25]

You want to power the Knee just for positioning, then the ratio could be whatever you needed to make it work, most use more than 4:1 for this, a photo of your machine would be good,are you sure you have a Ballscrew on the Knee Jack, most just had a acme screw thread

mactec, you're absolutely right, there's a 5 pitch ACME lead screw for the knee. Here's a picture of the BTC before the move...



Right now I have the mill apart to move / retrofit...

[jmille25]

I have recently replaced the DC servos on my Enco BP clone with DMM 750W ac servos. I used the same mounts and 2:1 bet drive on the X and Y. I use a 750W on my Z which is the knee. This has a 5:1 planetary gear drive with a 1:1 belt. I am still woking with motor tuning but have 120ipm on X and Y and 80 on the Z. The most I could get with the DC drives was 60ipm and 45 so I am quite pleased so far. Still have to get the spindle hooked up and do some cutting. Somany projects, so little time.

I'm really hoping for rapids in the range of 300IPM for XY...according to the manual the BTC could rapid at 295IPM XY and 200IPM in Z (quill), but maybe I should be reevaluating my expectations...

[mactec54]

I'm really hoping for rapids in the range of 300IPM for XY...according to the manual the BTC could rapid at 295IPM XY and 200IPM in Z (quill), but maybe I should be reevaluating my expectations...

Your will have your rapids of 300 IPM or very close to it, if you use the Dyna 4 Drives, this will give you the max motor RPM, if using the Dyna 2 Drives you will only get to about 160 IPM depending on what voltage power supply is used, if you can change your drive pulleys on the X and Y to 1 1/2 : 1 instead of the 2 : 1 you will get close to 400 IPM, they don't need to be 2 : 1 I run them at 1 : 1 on all the Boss 5 machines which is there standard gearing ratio, they only went to a 2 : 1 ratio to get a better machine resolution, with using the Dmm encoder, won't have a resolution problem

I used to have a Boss 5 running at 750 IPM this is too fast for this type of Ballscrew configuration, so don't recommend going over 450 IPM X and Y axes, if you want your machine to last, I still have one Boss 5 that I use just for testing different setups controls servo motors Drives Etc

Your Iron is the same as the Boss 5, just different top end with the tool changer, which are quite cool when you get them working right

[jmille25]

...you can change your drive pulleys on the X and Y to 1 1/2 : 1 instead of the 2 : 1 you will get close to 400 IPM, they don't need to be 2 : 1 I run them at 1 : 1 on all the Boss 5 machines which is there standard gearing ratio, they only went to a 2 : 1 ratio to get a better machine resolution, with using the Dmm encoder, won't have a resolution problem

That's an interesting thought...I had not considered changing the gear ratio. That could save a fair bit of time with not having to make bushings to adapt the old pulleys to the servos. I'll have to do some checking to find out what type of belt the BTC uses.

mactec, is it safe to assume you're only changing the pulley on the servo and not the one on the ballscrew as well? Can't say I've looked closely at the ones on the ballscrews...

[mactec54]

That's an interesting thought...I had not considered changing the gear ratio. That could save a fair bit of time with not having to make bushings to adapt the old pulleys to the servos. I'll have to do some checking to find out what type of belt the BTC uses.

mactec, is it safe to assume you're only changing the pulley on the servo and not the one on the ballscrew as well? Can't say I've looked closely at the ones on the ballscrews...

Yes that should be the best place to change it, you would not want to change the X axes or the Z axes Ballscrew, timing pulley, the Timing pulleys are H series .5 Pitch, if yours is the same as other Bridgeports of this vintage, some had a round tooth profile also, but the H series was mostly used, you can sometimes get them on Ebay so look around for what you need, Here is one supplier, there are many for this old profile

Photo of one I made

Timing Belt Pulleys & Timing Belts - Synchronous Drive Parts | B&B Manufacturing

[jmille25]

Photo of one I made

How did you go about making that? Are the two halves screwed together and the flanges pressed on?

Also, do you have any opinion on whether low inertia or medium inertia servos would be better for this application?

[mactec54]

How did you go about making that? Are the two halves screwed together and the flanges pressed on?

Also, do you have any opinion on whether low inertia or medium inertia servos would be better for this application?

Yes that one was made is 2 parts the flanges are staked/rolled on but i use a carbide ball for that and use a cnc machine to form the stake, here are some more photos of the same pulley, don't have one of just the staking

Either motor will be fine on these machine, low inertia is always the best choice, but can be harder to tune when you are dealing with machines like this, I would not worry about motor tech to much for these machines, the part that is the most important to do with the motor is the Encoder, and at 16 Bit you will have a smooth running machine

[dynoluc]

go with 750W servos