Chris G0704 Build

[ChrisAttebery]

Back in October of 2012 I started a G0704 build thread on CNC Zone. The Benchtop Mills forum over there is practically dead so I thought I'd start a thread here.

Chris G0704 Build on CNCZone.com

To catch up the machine has the following:
CNC Fusion Premium Ball Screw kit.
3 x KL-5056D Digital Bipolar Stepper Motor Driver-32 bit DSP Based
3 x NEMA23 570oz/in 5A 3/8” Dual Shaft Stepper Motor (KL23H2100-50-4B)
1 x 48VDC/12.5A Switching CNC Power Supply
Ethernet Smooth Stepper
CNC4PC C35 - QUICK SETUP BREAKOUT BOARD
CNC4PC C6 - Variable Speed Control Board
Manual Oiler
Vista CNC iMach P1A-S pendant
Mach Standard Mill running on Mach3.
Touch plate for MSM automatic tool offset measurement
2" head and column spacers.
ABEC 5 AC spindle bearing upgrade
Home brew fogless mist cooling system
1100W 4500rpm motor. IMHO the bare minimum for a decent CNC conversion.
KBIC-225 DC motor controller

2 speed belt drive. Based on Hoss' design. I wound up turning a pair of Multi V pulleys using a J6 belt. 3:2 high ratio and 1:2 low ratio. With the 1100W motor I wound up with 6750 rpm in high and 2250 rpm in low. The spindle pulley is a light press fit into a 6007 bearing. I turned a bushing to fit that bearing into the head casting. This setup is MUCH quieter than the L belts that I started out with.

 

[ChrisAttebery]

I made a full enclosure using TNUTZ 1010 rails and brackets. I used 1/4" Lexan for the front panels and sliding door. I just used Coroplast for the back walls. The machine sits on a steel stand that I welded up using 3/16 wall 2x3 and 2x2 tubing.

 

[ChrisAttebery]

That's basically where the machine was up until last week. On Thursday I was milling a block of steel that was going to run for a few hours. I was running a 1/4" 4 flute carbide end mill at 6000 rpm, .250 DOC x .020" WOC. The machine should have only been using about 1/3 HP but apparently I had abused it for too long and it melted down. It shorted out internally and smoked the KBIC in the process. Of course this happened when I had 6 orders sitting on the bench waiting to be machined over the weekend.

On Friday I ordered a MTRP-002-3BD36 2hp, 3600rpm 3 phase motor and a WEG Electric CFW300 series vector drive from Automation Direct.

I bored my motor pulley to .626 on my lathe. I didn't have any small HSS so I just used a piece of sharpened HRS in a tool block to cut the key slot.

 

[ChrisAttebery]

I’m in a tight spot since I don’t have a motor for the mill so I can’t machine a new mount. I decided to model the top of the machine in Fusion 360 and see what I could come up with. I realized that if I turn the motor 45 degrees that the bolts will clear the outside of the head. I made a couple plates from 3/16” steel on my drill press to mount to the head and turned a couple spacers out of 1” CRS on the lathe. This will move the motor 1” farther back than the 1100W motor but it will still clear the column but about 1/4”.

 

[ChrisAttebery]

I received my shipment from Automation Direct yesterday. They shipped everything FedEx Overnight. That was a nice bonus.

I was able to get the VFD wired up to the controller and motor. Programmed the VFD and was able to start the motor from Mach3. I programmed the VFD to give the motor a 4500rpm top speed so that it matches the 1100w motor it's replacing. That way I can reuse all of my G code.

I got the pulley fitted. The key slot was a PITA and needed to be filed about a dozen times.

Here’s a side by side picture with the new motor and the 1100w motor. It’s roughly twice the size.



Here's the new motor sitting on the head. The belts should be here this afternoon. I need to grab a couple 3/8-16 x 3" SHCS screws from the hardware store.

 

[Reddinr]

Well done. Always good to see machine build/conversion/rebuild projects I can selfishly learn from! I bet you will just feel better not having to baby the motor anymore. I've been thinking about converting my RF-45 type cnc mill to belt drive so I can get higher RPM and quieter operation. I just have not gotten up the nerve to tear down a perfectly fairly good machine yet. For now, for high RPMs I rig a porter-cable router to the head and that has worked OK for some things.

I have a, now dusty, ethernet smoothstepper that I figured I would implement at the same time. I need to figure out what kind of bearings to use for the spindle. I want to keep or improve the spindle run-out I have now but get it as fast as practical.

 

[ChrisAttebery]

The belts came in so I got the machine put back together. I ran a batch of parts for about an hour. The motor was at 105F, about 20 degrees above ambient. On these parts I use a 3 flute 3/8 end mill at 6750 rpm, .650” DOC and .030” WOC. The finish looks better. It think the old motor was struggling to keep up.

 

[ChrisAttebery]

Yesterday I took it easy on the first part but after that I went right back to the speeds and feeds I used with the 1100w motor.

Some observations:
1. The motor is quiet below 3500 rpm. As in with hearing protection it’s hard to hear it. Above 3500 rpm the fan is the dominant sound. It isn’t bad though. It’s kind of a low woosh sound.

2. I set the accel and deccel to 1 second each. I immediately noticed how much quicker the spindle ramps up and down compared the the DC motor setup. No more waiting for the spindle to stop before I change tools.

3. I had some parts that I started with the old motor and the finish seems to be better now. I think the old motor may have been struggling for a while.

4. After an hour of running non stop the motor was only about 25 degrees warmer than ambient. The old motor would have been 70-80 degrees over ambient.

5. Even though I have more power I don’t think I can push the machine any harder. I tried increasing the feed rate on one of my roughing cuts and I could hear the machine start to chatter and vibration levels increase. I think 1.5 cubic inches per minute in aluminum is about the limit for these machines. They just aren’t stiff enough to handle more than that. One exception is drilling. I had limited myself to 1/4” and below with the old motor and high speed belt drive. I should be able to push 3/8”-1/2” drills in the high speed setting now since the motor has constant torque down to 1350 rpm at the spindle.

 

[GunsOfNavarone]

I gotta ask as I am ready to do something now...
What does it cost to do this kind of conversion? The little I have checked into makes me want to buy a Tormach or..... instead of converting what I have. I assume the ballscrews have completely eliminated the backlash? There is the learning curve as well. I'm jealous! Great work! I really think something like this is more than I want to bite off. The VFD conversion wan't bad on my lathe, but this is FAR more entailed.

 

[ChrisAttebery]

Someone on the other forum mentioned that he regularly pushes his machine 2x harder than I've been pushing mine (3.4 cu in/min vs 1.5cu in/min). I took a look at my mill this morning. The screws all seem to be tight but I could feel some slop in the table if I grabbed the ends and pushed them in opposite directions.

The Y axis seemed to be the culprit. I was able to tighten it down quite a bit. It was enough that I decided to pull the gibb and take a look at it. There's a wear mark where the very top of the dovetail on the base is touching the gibb. It doesn't look like they are machined on the same angles. After playing with it for a while I got it about as tight as I can without stalling the axis. I think the only cure for this would be to buy a new gibb and grind or scrape it to fit the casting.

The X axis seems OK. I pulled the gibb and there are a few spots over the entire face that are contacting. It's not a lot and it's not very even, but it's better than the Y. I tightened it down until the screw bottomed out in the casting. That axis seems to be OK though.

I checked Grizzly's web site and the gibbs are available for $8.50 each. I think I'll order a pair and see if I can get a better fit on the machine.

Anyway I'm going to try pushing the MRR a bit harder over the weekend and see how the machine reacts.