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New Guy, New Mill (pm940)
- Thread starter mrbasher
- Start date
Here's another bit of info, helps validate my Z axis choice, maybe...
The mill came with a Z lift motor. The motor is a 120w, 1700 rpm motor with a 10:1 gearbox on it. Who knows if it actually outputs that much, but lets go with it. The model is 90YYJ-120 .Looks like a nice motor actually, I'm sure I can find a use for it.
So that's 120w at 1700rpm, which gives us .6779 Nm of torque. With the 10:1 reduction, that's 6.779 Nm of torque (but sloooow)
The Z servo I chose is 8.27 Nm rated, 23.3 Nm max. 1500 rpm rated, 3000 rpm max.
So, at a minimum, it should be able to lift it direct drive and at speed. Stop me if I'm thinking about this incorrectly.
The mill came with a Z lift motor. The motor is a 120w, 1700 rpm motor with a 10:1 gearbox on it. Who knows if it actually outputs that much, but lets go with it. The model is 90YYJ-120 .Looks like a nice motor actually, I'm sure I can find a use for it.
So that's 120w at 1700rpm, which gives us .6779 Nm of torque. With the 10:1 reduction, that's 6.779 Nm of torque (but sloooow)
The Z servo I chose is 8.27 Nm rated, 23.3 Nm max. 1500 rpm rated, 3000 rpm max.
So, at a minimum, it should be able to lift it direct drive and at speed. Stop me if I'm thinking about this incorrectly.
- Joined
- Dec 3, 2013
- Messages
- 1,844
Send me a PM with your email and I will send you my Solidworks files of my mill. You can compare dimensions and see how I approached things. I didn't have room to direct drive the X&Y so I used 1:1 timing pulleys.
When I was helping the high school build a CNC router I drilled the 3" x 3" x 1/2" aluminum angle stock that attached the main 2" x 6" X axis rails to the table. There were 6 sets of 4 holes 15" apart. I drilled the first 2 sets of holes on the mill and then used an alignment pin to index the stock for each remaining 4 sets of holes. We had a 0.015" tolerance over the 78". The 2" x 6" rails were drilled by one of the manufacturing sponsors, who makes satallite parts for NASA, on their large CNC mill with a 60" x 120" bed so I know those were spot on. The holes I did on my will were within 0.005" of the Sponsors holes so my error over 15" was no more than o.oo1".
The Z axis has a little more error due the the compromise between gib tension and head nod. Repeat ability is good for large movements but small movements, especially down, can have greater error due to the gib stiction. Next year I plan on tearing down the column and having the sides milled to accept linear rails to support the head to eliminate the nod and free up a gib tension a little. I toyed with a counter balance system hung toward the front of the head but it required more space behind the mill than I have.
When I was helping the high school build a CNC router I drilled the 3" x 3" x 1/2" aluminum angle stock that attached the main 2" x 6" X axis rails to the table. There were 6 sets of 4 holes 15" apart. I drilled the first 2 sets of holes on the mill and then used an alignment pin to index the stock for each remaining 4 sets of holes. We had a 0.015" tolerance over the 78". The 2" x 6" rails were drilled by one of the manufacturing sponsors, who makes satallite parts for NASA, on their large CNC mill with a 60" x 120" bed so I know those were spot on. The holes I did on my will were within 0.005" of the Sponsors holes so my error over 15" was no more than o.oo1".
The Z axis has a little more error due the the compromise between gib tension and head nod. Repeat ability is good for large movements but small movements, especially down, can have greater error due to the gib stiction. Next year I plan on tearing down the column and having the sides milled to accept linear rails to support the head to eliminate the nod and free up a gib tension a little. I toyed with a counter balance system hung toward the front of the head but it required more space behind the mill than I have.
My mill (PM-932) has 1605 screws on the X and Y and a 2005 on the Z. The original installation used single ballnuts and these worked well for the past year and a half. The downside was backlash on the Y axis was .0018" and X was .0035". So I opted to go with double ballnuts from Linear Motion Bearings. I'm installing them now and hopefully will have the machine running in a couple of days. I'll post the backlash findings in a few days.
I hope i answered your questions.
Tom S.
I hope i answered your questions.
Tom S.
Got my mill back together and operational today. After fiddling with AC bearing preload I ended up with about .0005" backlash on X and Y. The Z axis has about .003". Not sure if it makes sense to spend more time trying to get it closer to zero as my motor standoff and AC bearing housing design is a pain to disassemble and reassemble. Next step is to adjust the gibs. Played with the Y gib a bit but not having much luck getting consistent dial indicator readings. There's always tomorrow.
Tom S.
- Joined
- Feb 8, 2014
- Messages
- 11,145
If you can preload the Z-axis in one direction or the other with a counter balance, you should be able to get that to zero backlash.
So, I did some checking today on my CNC router, Just because well, I never have...
Using an Interapid .0005" indicator, I'm seeing almost no backlash. Granted, it's not a 10ths indicator, but you can infer quite a bit with it. As well, the router places very little strain on the axis. I also did some checking of the ball screw error over 12". Unfortunately, I was using an iGaging Absolute scale and after some recent machining I don't trust them much. I wouldn't buy them again. Anyhow, I showed about .007" error. It might be right, it might not. I'm going to test another way.
That said, based on what I've seen, I'm going to go with the Chinese C7 ball screws and see how things go. I'd guess the ones on the router aren't much different. They are rolled.
Jbolt, thank you for the files, they work perfectly. Sorry I haven't had a chance the respond via email yet. Too many irons in the fire and too many 2 year olds and under running around. (2)
On another note... I had a great, well I think, idea for a "speeder" spindle as Tormach calls it. More on that later. Should be simple to do once the conversion is done and I can do the mounts with CNC.
Using an Interapid .0005" indicator, I'm seeing almost no backlash. Granted, it's not a 10ths indicator, but you can infer quite a bit with it. As well, the router places very little strain on the axis. I also did some checking of the ball screw error over 12". Unfortunately, I was using an iGaging Absolute scale and after some recent machining I don't trust them much. I wouldn't buy them again. Anyhow, I showed about .007" error. It might be right, it might not. I'm going to test another way.
That said, based on what I've seen, I'm going to go with the Chinese C7 ball screws and see how things go. I'd guess the ones on the router aren't much different. They are rolled.
Jbolt, thank you for the files, they work perfectly. Sorry I haven't had a chance the respond via email yet. Too many irons in the fire and too many 2 year olds and under running around.
(2)On another note... I had a great, well I think, idea for a "speeder" spindle as Tormach calls it. More on that later. Should be simple to do once the conversion is done and I can do the mounts with CNC.
Well I've officially dived in head first... (Dove? Don't think that's right)
I ordered Mesa 7I77-5I25 kit as well as my servos and drivers from DMM. DMM has been very helpful. We're even talking about some simulation applications for their equipment. Anyhow, I have 750 watt servos for x and y coming as well as a 1.3 kilowatt servo for Z. So, now I have an axis with a motor more powerful than my spindle... Haha! All of the drivers are DYN4 drivers. These should give me all the control I want/need. I'm a geek so I couldn't resist. Plus I had to get one for the Z servo anyhow. Their power supplies are integrated, making things less messy.
This is getting exciting. Just not sure when I'm going to work on it... I suppose after the kiddos go to bed every night and before I fill orders for the next day... Yikes.
I ordered Mesa 7I77-5I25 kit as well as my servos and drivers from DMM. DMM has been very helpful. We're even talking about some simulation applications for their equipment. Anyhow, I have 750 watt servos for x and y coming as well as a 1.3 kilowatt servo for Z. So, now I have an axis with a motor more powerful than my spindle... Haha! All of the drivers are DYN4 drivers. These should give me all the control I want/need. I'm a geek so I couldn't resist. Plus I had to get one for the Z servo anyhow. Their power supplies are integrated, making things less messy.
This is getting exciting. Just not sure when I'm going to work on it... I suppose after the kiddos go to bed every night and before I fill orders for the next day... Yikes.
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