Turning speed

[kubotaman]

Okay being new to the indexer scene I have a question. Is it possible to either slow down the feed rate or speed up the turning speed while exicuting a file made in the Shopbot program. If so how???

[rcnewcomb]

I'm not at my machine, but don't Shift> and Shift< work?

To change it within the program you would use the VS command. (MS only changes XY, and Z, not A or B)

[myxpykalix]

Unless i am mistaken this is kind of similar to what i asked about over a year ago:

http://www.talkshopbot.com/forum/showthread.php?t=1470&highlight=Attn

Although my purposes and uses would be a bit different, however once you create a file you cannot speed up the feed or rotation while a file is running (assuming you are talking about a indexer file). For that you would need independant axis control and so far i haven't heard whether that had been implemented. My understanding was it was a small software fix and a possible addition of a small card but i don't recall the specifics.

However if what you are trying to do is speed up a rounding operation that would help you but if you are trying to speed up any type of carving You would have to be able to speed up both feed and speed and rotation and i'm not so sure you would be able to do that sucessfully.

But then again this wouldn't be the first time i was wrong, and won't be the last!:eek:

[waynelocke]

As Randall wrote you can speed up or slow down the x speed while the file is running with shift < or shift >. You can pause the file and choose insert command and do a vs to speed up or slow down the rotation then unpause the file.

[dana_swift]

The indexer (A & B) channels move speeds need to be controllable from the keyboard during cutting just like X and Y's move speeds. Put this in the "feature request" category..

Perhaps have a mode where the indexer move speeds change in proportion at the same time using the shift < and >, that way the indexer will stay in sync with the gantry/table motion at the new move speed.

"Thinking out loud"..

D

[oddcoach]

you can manually enter the MS,,, command into the file if you know where you want to make the change. or hit the space bar while the file is running and insert it there

[kubotaman]

I could be wrong but aren't turning speds and x axis go hand in hand during cutting on the indexer? In other words if I speed up the x axis it automatically speeds up the B axis?

[myxpykalix]

I seem to be learning soming here myself, but I am pretty sure the answer to your question is NO that if you speed up the X axis the B will compensate and spin faster.

That was what i was talking about with independant axis control and why i didn't think you could control the speed of a already running file. What i may be misunderstanding about their responses is if these commands (VS) is something you can do on a running file or something to change the normal rotational speed prior to starting a file. I may be misunderstanding, so i'm going to have to go out and try some of these...

[oddcoach]

I have found that you can change the X speed all you want and it really does not do much. the rotational speed makes all the difference. Jack you can change the speed on a file that is already running. Hit the space bar and the file pauses then choose insert command then vs for speed values then change the value for your rotational axis. the speed returns to the original value when the file is finished cutting.

[kubotaman]

Okay here is an example of what I am talking about. Today I wrote a quick file. I told the b axis to spin at a given speed and also lower the z axis at the same time. If I would make the b axis spin fast the z axis would lower down at a fast rate. If I spun the b axis at a slow speed the z axis would lower much slower! It seems to me that the B axis runs all the other axis's, in regards to movement when in motion!! Try it out and see if I am wrong or right.

[jdervin]

Okay here is an example of what I am talking about. Today I wrote a quick file. I told the b axis to spin at a given speed and also lower the z axis at the same time. If I would make the b axis spin fast the z axis would lower down at a fast rate. If I spun the b axis at a slow speed the z axis would lower much slower! It seems to me that the B axis runs all the other axis's, in regards to movement when in motion!! Try it out and see if I am wrong or right.

Daryl--

Could you share with us your quick file? Similarly, what were some of your speed combinations? Knowing this might help in calculating the results.

I think a clue to finding an answer possibly lies within this quote from the ShopBot User Guide:

"...the speed of the motors change as the tool moves... This is as it should be. The changing motor speed occurs in order to maintain a constant vectored speed of the cutter..."

In other words, the software is trying to automatically move the cutter at a constant speed in the direction of travel, which may or may not be parallel to any one specific axis. For instance, as I understand it, cutting a 45° angled line, with an X/Y move speed of 2" per second, will limit both motors to running at ~1.41" per second. I presume that the Z-axis is automatically calculated in the same manner. Since the B-axis is essentially replacing either the X or Y-axis (depending on which way your indexer is set up), the same theory would apply -- except that the B-axis is moving in degrees per second and is therefore much more sensitive to variations in speed.

My best guess? The speed of the B-axis may not be "running" the speed of the Z-axis, but it may be limiting it from reaching its maximum speed. Ramping is also probably playing a role.

[Brady Watson]

If I would make the b axis spin fast the z axis would lower down at a fast rate. If I spun the b axis at a slow speed the z axis would lower much slower! It seems to me that the B axis runs all the other axis's, in regards to movement when in motion!! Try it out and see if I am wrong or right.

This really only holds true when you are doing a multi-axis move, such as an XB, ZB or XZB move where the turning of the B-axis MUST be completely synchronized to the other axis to make the cut.

If the tool seems soggy or lagging while it is making these types of moves, then you need to tighten up some of your ramp settings to reduce this. Also, there should not be a large disparity between your set XY,Z & B speeds. YOU should make yourself a chart of useful speeds that seem to work well for the type of work that you do.

Naturally, a 3D indexer file that rasters in the X and is incrementally stepped over via the B axis runs & ramps completely differently than (what I call) a 2D indexer file that cuts text in a helical pattern around the circumference of the material blank.

You may find it helpful when gauging move speeds on the indexer to think in terms of inches. If you are running a 4" dia blank and you set your VS to 180 degrees per second, you are running (C = pi x dia) C = 3.1416 x 4 = 12.5 / (180 deg / 360 deg) = 6.25 surface inches per second! If you had a 12" diameter part, you would be moving through the material at the outer edge at a rate of 18.8 inches per second (!) if your VS was set to 180 degrees per second.

You REALLY need to think about the mechanical work that you want to do - and then set your rotation speed accordingly. As you can see from the calculations above, the exact same rotational speed of 180 deg/sec results in VERY different surface speeds depending on the diameter of the part being cut.

-B

[blackhawk]

Brady brings up a good point on the surface speed calculation. I am working on my own indexer using a stepper hooked to a regular lathe. I was wondering where to start out on the B axis speed. If you look in the control software, the default move speed on the B axis is 720. In Brady's example, this would translate into 25 surface inches per second!!!!!:eek:

Why is the default set so high? Where do some of you other guys with indexers have your move and jog speeds set at?

[myxpykalix]

I might be rusty and sleepy but 720 would refer to only 2 relovutions correct? When you are working with the indexer you are dealing in degrees (360=1 revolution) not inches like on the table.

[jdervin]

For turning rings, blanks, or very fine spirals I use the following formula to convert my X/Y-move speed to a B-move speed in degrees:

B = M × 360 / (2πR)

Where:
B is the B-move speed in degrees
M is the XY-move speed in inches per second
and
R is the radius of the piece being turned

Since the radius will always be different at any given depth, I go with the maximum radius, but for deep cuts, it might be worth adding a speed change command within the cutting file.

The formula gets a bit more complicated for coarse spirals and I think it looks something like this, though more mathematically inclined people than I can probably simplify it:

B = M × (sin(atan((2πR)/(L/W)))) × 360 / (2πR)

Where:
B is the B-move speed in degrees
L is the turning pattern length
M is the XY-move speed in inches per second
R is the radius of the piece being turned
and
W is the number of times the pattern wraps around the blank

[blackhawk]

John - Thanks, that makes sense with what Brady was saying. With your first formula with a 4" diameter and 3 inch/sec X and Y, you get 86 for the indexer speed. I turned a 2" blank last night with my speed at 180 and that worked out good for me. The 180 gave me a surface speed just over 3 inch/sec.

Also John, I am a Pi*D man myself. I don't like those radii.:)

Jack - 720 is 2 revolutions, but we are converting the rotational speed of the blank into surface feet per minute. The (2*pi*r), or as I like (pi*d), is just the formula for the circumference of a circle. This just relates the cutting speed back to a linear motion.