Fehlmann Picomax 50 CNC conversion/refurb

[Agathon]

[QUOTE=m_c;92790][pedant mode] The motor should have the same torque at any speed provided the VFD is not limiting current. It's the lack of gearing that means there is insufficient torque at the spindle[/pedant mode]

While I don't claim any expertise on inverter drives, I've been using them for the last 20 years and my understanding and experience is that torque falls off either side of the nameplate frequency. Modern motors designed for inverters and "vector control" improve the flatness of the torque curve but the reason machine tool manufacturers using this type of drive specify such huge motors is due to the drop-off in torque. As an example, one of the Swiss firms I represent in the UK make a plain lathe of 70mm centre height designed for instrument making and horological work. The spindle is belt driven at 1:1 by a inverter controlled 1.1kW motor. In the past this machine was made with multi-pulley drive with a fixed speed motor of 300W!!!

I hadn't understood the four contactors for speed were operating a mechanical device, I thought you were using the inverter digital inputs to select four preset speeds.

You may have provoked me into boring you all with another video! The contactors just control the 4 motor speeds nothing mechanical. The variator (Reedes drive) gives the mechanical variation.

[EddyCurrent]

I hadn't understood the four contactors for speed were operating a mechanical device, I thought you were using the inverter digital inputs to select four preset speeds.

[Robin Hewitt]

I feel your pain. I got the notion that everyone was getting better performance out of stepper motors than me and I now have 3.4's which I drive at 220 Volts. Problem is they run hot and I don't trust them at full tilt which is strangely self defeating. You can't win. I keep thinking servo motors are the way to go but I have always been just one rebuild away from wonderful so I am not convinced. Do you really need mega speeds? What is the max delay, end to end on the table? Is it really a problem?

I suspect the reason we can't have nice stepper motors is that someone has decided they must all be 200 full steps per rev. I got a Roland mill which had 400 full step/rev motors and it is freakin' amazing.

You are blessed to have that quick tool release, but I am not so sure about driving the Z through the quill rack. I put a ball screw to drive the Z, a ball screw that has to be released every time I hammer out taper tooling. It's only one M8 cap head but I've already had to helicoil the thread.

[EddyCurrent]

You should have a look at Mach3 Brains, watch this video to get an overview; https://www.youtube.com/watch?v=O8V7dZy02og

[Agathon]

I feel your pain. I got the notion that everyone was getting better performance out of stepper motors than me and I now have 3.4's which I drive at 220 Volts. Problem is they run hot and I don't trust them at full tilt which is strangely self defeating. You can't win. I keep thinking servo motors are the way to go but I have always been just one rebuild away from wonderful so I am not convinced. Do you really need mega speeds? What is the max delay, end to end on the table? Is it really a problem?

I suspect the reason we can't have nice stepper motors is that someone has decided they must all be 200 full steps per rev. I got a Roland mill which had 400 full step/rev motors and it is freakin' amazing.

You are blessed to have that quick tool release, but I am not so sure about driving the Z through the quill rack. I put a ball screw to drive the Z, a ball screw that has to be released every time I hammer out taper tooling. It's only one M8 cap head but I've already had to helicoil the thread.

Thanks for the empathy - much needed! I think the thing is that most people are building routers with very low friction linear rails and low mass tables/gantries. What I've got here is a beast compared to a CNC router. In fact it's probably one of the lightest and smallest pro CNCs that was built. Since owning this machine I've been looking at other high quality, but old, CNCs with a view to doing the same thing, but these are all massive for the same envelope that the Fehlmann has. A couple of good Deckel CNCs have sold on eBay recently for just over a grand but you're talking about 2-4 tonnes of iron, which I don't have the space or the heart to be involved with. Maybe I'll eventually replace my manual Aciera F4 with a bigger CNC, but for now I'll sit tight.

You are quite right about the traverse speed. The afore-mentioned Aciera F4 has a rapid of 1800mm/min which has never made me feel like I need to pop the kettle on while it does its stuff. So 2000mm/min is fine on the Fehlmann - if it can do it reliably.

Having been involved with very high-quality manual machine-tools for a very long time I tend to want a professional solution to a problem. It's been a steep learning curve, but as I see it stepper motors for machine tools are now really an amateur thing. I want this machine to perform as an industrial machine should and I will be using it to produce high precision stuff for my own amusement and for my business (I say business, it's Halcyon-days are behind it and with things as they are at the moment it's a paying hobby, which isn't such a problem as I have another job too). Hence, I am drawn to servo motors. The only problem is I know sweet FA about them!

I'll see how driving the rack goes. As I said in the vid, this thing is a very high precision thing and I can detect no backlash in the rack. There must be some of course, but it's certainly less than 0.01mm. Fehlmann developed this machine into a 3-axis a year or two later and drove the rack with a servo motor - they seemed to have sold quite a few of these machines and they are still sought after in Switzerland.

Hammering-out taper tooling is always bad news. Have you thought about making a captivated draw-bar so that it pushes the tooling out as you unscrew it?