[dwalsh62]

From the IH web site:

Our Turnkey 3 axis CNC Mill uses 410 in/oz peak motors on the X and Y axis.
The drive ratio is 4:1. So the ballscrew sees 1640 in/oz of torque.
Our math: 410 in/oz x 4 = 1640 in/oz

The Z-Axis uses a 648 in/oz x 4 = 2592 in/oz

So the 507 in-oz motors from DMM at a 3:1 ratio would give me 1521 in-oz.
With a 5mm (.20") lead screw that equals 3000 rpm / 3 = 1000 rpm.

1000 rpm x .20 = 200ipm rapids.

Using the theoretical values is not considered good engineering practice, practical values are 0.92 of the theoretical value and is the preferred value that should be used when calculating power.

Also, the 5mm metric screws only have 0.196in lead, not 0.200in lead, a common mistake made by many it seems.


If you want a 0.200in lead screw then I recommend you buy an appropriate screw.

[skray775]

Very interesting... My current machine uses the 300 watt motors rated at 3000RPM and the same 5mm ball screw lead.

Max rapids are 187

200 IPM x.92 = 184

Using the theoretical values is not considered good engineering practice, practical values are 0.92 of the theoretical value and is the preferred value that should be used when calculating power.

Also, the 5mm metric screws only have 0.196in lead, not 0.200in lead, a common mistake made by many it seems.


If you want a 0.200in lead screw then I recommend you buy an appropriate screw.

[dwalsh62]

Very interesting... My current machine uses the 300 watt motors rated at 3000RPM and the same 5mm ball screw lead.

Max rapids are 187

200 IPM x.92 = 184

That is all wrong if you calculated 200IPM for a 5mm lead screw and used 0.200in as the lead value.

If you calculated anything based on 0.200in lead when using a 5mm lead screw your values will be incorrect, a metric screw with a 5mm lead is 0.196in.

You might wonder "Why is a Theoretical Factor (TF) used"?

If you build 5 machines using the same identical parts and then measured IPM and Torque you would find they are all different but should never fall below the advertised values which is calculated based on the Theoretical Factor (TF).

The standard design TF is 0.92% however some manufacturers use a lower value like 0.75% to de-rate the specifications to increase MTBF if the end user never pushes the product beyond the advertised specifications.

If you want to know what your motor torque requirement is you estimate your required torque then calculate it with the following (assuming a reduction of 3:1).
Design Torque Calculation: (Estimated Required Torque / TF) / Ratio
1100 / 0.92 / 3 = 398.5507oz/in

Some more calculations, let's start with a 400oz/in motor and a 3:1 reduction ratio.

Advertised Torque Calculation: (Torque x Ratio) x TF
(400 x 3) x 0.92 = 1104oz/in.
If you get a higher (measured) torque value them your $hit is better quality but worst case scenario will be this value which would be the manufacturers advertised torque specification.

Advertised IPM Calculation: ((RPM / Ratio) x Distance) x TF
((3000 / 3) x 0.196) x 0.92 = 180.23.
If you get a higher (measured) IPM them your $hit is better quality but worst case scenario will be this value which would be the manufacturers advertised IPM specification.

If you only get a max feed rate of 187 using a 3000RPM motor and a 3:1 reduction ration, you are above the theoretical feed rate 180 (always round values down) then I would say your machine is working optimally.

If you want to guarantee a 200IPM feed rate then design for (200 / 0.92 =) 217.3913 (or higher)

[skray775]

The machine was delayed and should arrive in a few days.

DMM has quoted $1100.00 for 3 axis drives, motors, power supplies, cables, estop, limit switches shipped. I will order that soon.

I will use LMB ball screws and order those after I draw up the mounting system.

I am going to use a Fabco 4 stage ait cylinder for a power draw bar but need to figure out the right one. I also need to choose a VFD for the 3 phase motor.

[gd.marsh]

Kelly,

Don't know if you've seen this but should be the info you need to determine which Fabco cylinder you want ..
http://www.fabco-air.com/pdf/Sec_5.pdf

On the VFD. I started with a Teco 7300CV (which several others seem to also be using) .. mine died on me while under warranty so I got a refund & bought a Hitachi SJ200 which is serving me well ..
Teco has a computer program for setting up the drive (interface is extra) but it makes it real easy to do .. The Hitachi is set up manually with buttons on the drive so takes a little longer but once it's set you won't touch it much anyway.

You ought to have a fine machine when done .. I am impressed with the outcome of your round column conversion.

Gary

[skray775]

Thank you Gary,
I will check out that Fabco link.

The machine arrived today and I was able to get it un-boxed and moved into the shop. This is one beefy machine!

Notice the picture with my small round column machines in the background! The MD001 is about twice the size of the Jet JMD15's.

Also take note of the yard stick I placed on the table for a scale!

[skray775]

I couldn't let it sit so I drained the oil, removed the motor, gears, head, and gear shift levelers.