Doing things backwards

Shotgun said:
I used the 34's on my Bridgeport Boss CNC. Stepperonline has closed loop 1700oz-in (12Nm) 34s for about $80.
It has been plenty enough to shatter a 5/8" carbide endmill. And it'll do 100ipm in its sleep. Personally, that is to fast for me, but the incremental step-up was so cheap. How could I not. As a point of reference, BP shipped this mill with ~650oz-in open loop steppers that were twice as large and weighed three times as much.
Whatever you do, go with the closed loop.
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Never used closed loop, does the "loop close" by a positional feedback loop back to the driver or does this also impact the G Code as well?
EDITED- it appears the feedback is to the controller so will have to see what the implications are.
 
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The implications are that you will have fewer ruined parts and broken endmills.
If the motor is not strong enough to do what your G-Code told it to do. . . it simply won't happen. The computer program is no wiser, and goes along it's merry way telling the motor to do other things. Except, now it is off track and is trying to plow a 1/4" endmill through an inch of steel. Now, you're part has the partial cut the endmill made before it snapped in two (or more) parts.
By closing the loop, the computer says move, and the motor tries. With the encoder it knows if it succeeded or not. It will try several more times, and if still not able, reports back that it stalled. The computer sees the alarm and stops (hopefully) before everything is a mess.
My steppers are configured to alarm if they get 1/2 a turn out of sync with the computer.
 
Turbine-Wine said:
Never used closed loop, does the "loop close" by a positional feedback loop back to the driver or does this also impact the G Code as well?
EDITED- it appears the feedback is to the controller so will have to see what the implications are.
Click to expand...
@Shotgun pointed out the benefits of closed loop systems.
Think of the checks and balances. The G-code is the command, which is developed with your CAM program (HSM, MasterCam, etc.) and it does not change during machining. The encoder is verifying whether the motors actually did what the G-code told them to do.

But... There are a lot of machines that use non-closed loop systems. For example, 3D printers do not use closed-loop systems (or, at least none that I am aware of) due to the cost and size of the motors. There are a lot of CNC machines used for wood cutting that only use steppers. That being said, I would not have a milling machine that does not have encoders for the reasons Shotgun pointed out.
 
I lived, which is good for my health :)
I got COVID a month ago. Got it bad, lost taste (some say I never had any) smell, and slept 18-20 hours a day for 2 weeks. I beat it but my "get up and go has got up and left". Still weak, but still able to buy things for the CNC part of this project. I should be able to start before Xmas but no idea when my "get up and go" comes back.
Its nice to know that even if on deaths door, you can still muster the strength to hit the Enter Button on Amazon :)
 
Question- I need to cut twocircular holes in a 6 inch box beam that are 3 5/8ths in diameter. I do not have a 4 inch Boring head, but I do have a 3 inch head. Is there any way to cut the holes other than buying a 4 inch head? If a 4 inch head is the best tool for the job, where is the best place to to buy one. I have looked at flycutter type bits but this will be a repetitive function. So I need something that will last, or, has lower cost to replace parts?
 
You have several options. Does your head have a cross-hole? both of mine do. This allows you to fix a boring bar horizontally in the head, and cut holes larger than the diameter of the head's range. Be careful about stick-out, especially for a small boring head, but you can get by with a HSS tool, very sharp, up to 5" in 3" heads with a bar horizontally.

boring bar.jpg
 
Dabbler said:
You have several options. Does your head have a cross-hole? both of mine do. This allows you to fix a boring bar horizontally in the head, and cut holes larger than the diameter of the head's range. Be careful about stick-out, especially for a small boring head, but you can get by with a HSS tool, very sharp, up to 5" in 3" heads with a bar horizontally.

View attachment 468841
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I ws wondering what that hole was for :) Yes I have the same design as yours.
I got a 12 pc kit with the machine and it was new and not used.
 

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Is there a rule of thumb for selecting a rotary table for a mill? If the table is 10x30 is a good idea to get a rotary table that is also 10" or should it be smaller than the mill table? A neighbor has an 8 inch for sale
 
Get the largest table you can handle and can afford. an 8" is the minimum in my opinion. Smaller ones are too small to clamp anything but the smallest of parts to... I have an 8" and a 10", but I should have bought a 12" for the work I do. So I made a 12" fixture plate that bolts to both my 8" and my 10" rotary tables.
 
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