- Joined
- Dec 3, 2013
- Messages
- 1,849
At the end of the day it really depends on what you will be making that will determine how much mill you need. This can be an almost impossible question to answer if you have no prior experience with a CNC mill. Often it comes down to budget and space.
The next question is do you want to build a CNC mill or just have a CNC mill to use? Building a mill takes some planning and time to complete. You will also need a mill and possible a lathe to make the parts for the conversion. I stripped, measured and reassembled my mill to use to make parts for the conversion.
The advantage to building a mill is being able to configure it to your own specifications / needs. You can control some of the over all costs by which components you use. If you would rather just get to making parts I would look at a commercial offering.
I converted a PM-932 to CNC about 5 years ago. My recommendation is to get the largest mill you can afford with the largest travels. More mass = more rigidity, larger cuts, better finishes and a larger work envelope. You can never have enough work space. The down side to a larger mill is everything else that goes along with the conversion is larger / costlier i.e. stepper/servos, drives, power supplies, ball screws etc.
A gear head is limited to about 3K rpms. This is due to the tapered roller bearings and the amount of heat a gear head will create. At the stock 2k rpms, running for several hours the head and spindle would get too hot to comfortably touch all the while shedding grease from the spindle bearings
As most everyone who has done a conversion on a gear head mill will tell you, spindle speed becomes a limiting factor pretty quickly. I did the 3 phase/VFD belt drive conversion and have up to 7K spindle speed with AC bearings on the spindle. I normally do not run over 6K due to the lower quality import 3ph motor/VFD I am using. With a quality motor/VFD/AC bearings some have run the spindles up to 10k.
With the belt drive I have two drive ranges depending on the belt/pulley location, 0-1750 rpm & 1750-7000 rpm. Steels are typically done at the lower speed range and aluminum at the higher. HP, spindle speed and machine rigidity will dictate how large or small a cutter you can use. I routinely use end mills from 1/8" to 3/4".
The next question is do you want to build a CNC mill or just have a CNC mill to use? Building a mill takes some planning and time to complete. You will also need a mill and possible a lathe to make the parts for the conversion. I stripped, measured and reassembled my mill to use to make parts for the conversion.
The advantage to building a mill is being able to configure it to your own specifications / needs. You can control some of the over all costs by which components you use. If you would rather just get to making parts I would look at a commercial offering.
I converted a PM-932 to CNC about 5 years ago. My recommendation is to get the largest mill you can afford with the largest travels. More mass = more rigidity, larger cuts, better finishes and a larger work envelope. You can never have enough work space. The down side to a larger mill is everything else that goes along with the conversion is larger / costlier i.e. stepper/servos, drives, power supplies, ball screws etc.
A gear head is limited to about 3K rpms. This is due to the tapered roller bearings and the amount of heat a gear head will create. At the stock 2k rpms, running for several hours the head and spindle would get too hot to comfortably touch all the while shedding grease from the spindle bearings
As most everyone who has done a conversion on a gear head mill will tell you, spindle speed becomes a limiting factor pretty quickly. I did the 3 phase/VFD belt drive conversion and have up to 7K spindle speed with AC bearings on the spindle. I normally do not run over 6K due to the lower quality import 3ph motor/VFD I am using. With a quality motor/VFD/AC bearings some have run the spindles up to 10k.
With the belt drive I have two drive ranges depending on the belt/pulley location, 0-1750 rpm & 1750-7000 rpm. Steels are typically done at the lower speed range and aluminum at the higher. HP, spindle speed and machine rigidity will dictate how large or small a cutter you can use. I routinely use end mills from 1/8" to 3/4".
