I'm new to this CAM thing. I'm using a Taig CNC desktop mill with a
Flashcut controller.
But I'm running into some problems trying to develop G code that can
work around the fixtures such as clamps or a vise that I need to use
to secure the stock for milling.
First I tried to use regions to control the area that gets milled,
but I ran into a problem where the tool didn't use the clearance
setting when doing rapid movement between cuts. After breaking off a
mill I discovered the "Engage/Retract" tab in Visual Mill and changed
the setting not to "skim" cut transfers.
But I'm wondering what other general strategies there are for
automated milling around fixtures. Some ideas that come to mind.
- Use regions to break up the project into sections, each of which is
clear of any obstructions. Then run them separately and perhaps shift
the hold down clamps between sections as needed.
- Model the obstruction, such as a vise, and use it as a precision
region template.
- Use more sophisticated and less obstructing hold-down methods. A
friend was telling me about some sort of double stick tape they use.
Also, are there any good forums or books that can be recommended
where these sorts of CAM and CAD issues are addressed? Especially in
the context of desktop CNC milling and rapid prototyping, etc.
Strategies and techniques to address these sorts of CNC problems
don't seem to be covered anywhere much.
Thanks,
- Richard Lawler
Looking for CAM strategies with VM
Looking for CAM strategies with VM
Hi Richard,
You're on the right track - keep trying things and find out what works for you. I have a bunch of books on machining but none I have really help you develop the actual machining strategies. Check out your local library or Amazon.com and type CAD CAM into the search box. You need to buy a couple of books to fill in all the blanks. My books tend to focus on hand coding (yuck) but do explain many things like climb milling and conventional and it is important you understand the differences as they both have their place. It also helps if you understand how to machine simples things manually.
Don't forget the tutorials, they are helpful to get you going. Basically you start with a big mill and work down to a little mill for the detail bits. You use the regions to only work with the small mills in the areas that require it. If you are designing your parts before you machine them, you will eventually learn how to design with a view to "manufacturability". That will make your machining a LOT easier. You'll become a better designer too. Practice in machineable wax - it is a lot less stressful when you're proving out a toolpath. It's also extremely helpful when learning about setting tool offsets during tool changes.
I have used (and still do use) regions as "keep out" areas but mostly I try to clamp the part from below whenever possible. I have used a vacuum fixture for some flat parts and good old 6" kurt vices with parallels or step jaws to space the part appropriately. Find a vice which will fit on a Taig - I don't think a 6" Kurt will... Hey a 6" vice probably weighs more than the complete Taig!)
An example: I clamp a part and let's say it is 25mm high and 4mm is being clamped in the vice. I set my Z0 at the top corner and set my "bottom" under the Parameters/Cut Level setting of MOPS to say -20.0mm Then I create the various MOPS and machine away. The mill will stay 1mm above the vice plane. Then, I flip the piece over and create a new tool path (new MOPS) using the previous bottom, now top to set my Z0. Depending on which way you have flipped you part, you also have to pick the appropriate X0 Y0 points. You may have to use an edge finder and maybe an end stop or maybe a 1x2x3 reference block to find your X0, Y0 points. I'm assuming you know how to zero your Tool #1 on the top of your part with a feeler gauge?
Now, your sides are already machined to 5mm below your "now" top. So now in VM, set the bottom (under Parameters/Cut Level) to say -5.0 or -5.25mm for example. Now machine away and your top and bottom will meet and if you've done it right, there will be no signs of a "join" line... (To be honest it took me quite a while to get it right, so practice!)
Alternately set your Z0 to the top of the vice spacer/parallels (the plane where the "now" bottom is sitting) and now your part top is +25.0mm. So set your bottom machining level to +20.0 or +19.75mm as per the above example.
Hope this helps and doesn't confuse you.
Cheers, Peter
You're on the right track - keep trying things and find out what works for you. I have a bunch of books on machining but none I have really help you develop the actual machining strategies. Check out your local library or Amazon.com and type CAD CAM into the search box. You need to buy a couple of books to fill in all the blanks. My books tend to focus on hand coding (yuck) but do explain many things like climb milling and conventional and it is important you understand the differences as they both have their place. It also helps if you understand how to machine simples things manually.
Don't forget the tutorials, they are helpful to get you going. Basically you start with a big mill and work down to a little mill for the detail bits. You use the regions to only work with the small mills in the areas that require it. If you are designing your parts before you machine them, you will eventually learn how to design with a view to "manufacturability". That will make your machining a LOT easier. You'll become a better designer too. Practice in machineable wax - it is a lot less stressful when you're proving out a toolpath. It's also extremely helpful when learning about setting tool offsets during tool changes.
I have used (and still do use) regions as "keep out" areas but mostly I try to clamp the part from below whenever possible. I have used a vacuum fixture for some flat parts and good old 6" kurt vices with parallels or step jaws to space the part appropriately. Find a vice which will fit on a Taig - I don't think a 6" Kurt will... Hey a 6" vice probably weighs more than the complete Taig!)
An example: I clamp a part and let's say it is 25mm high and 4mm is being clamped in the vice. I set my Z0 at the top corner and set my "bottom" under the Parameters/Cut Level setting of MOPS to say -20.0mm Then I create the various MOPS and machine away. The mill will stay 1mm above the vice plane. Then, I flip the piece over and create a new tool path (new MOPS) using the previous bottom, now top to set my Z0. Depending on which way you have flipped you part, you also have to pick the appropriate X0 Y0 points. You may have to use an edge finder and maybe an end stop or maybe a 1x2x3 reference block to find your X0, Y0 points. I'm assuming you know how to zero your Tool #1 on the top of your part with a feeler gauge?
Now, your sides are already machined to 5mm below your "now" top. So now in VM, set the bottom (under Parameters/Cut Level) to say -5.0 or -5.25mm for example. Now machine away and your top and bottom will meet and if you've done it right, there will be no signs of a "join" line... (To be honest it took me quite a while to get it right, so practice!)
Alternately set your Z0 to the top of the vice spacer/parallels (the plane where the "now" bottom is sitting) and now your part top is +25.0mm. So set your bottom machining level to +20.0 or +19.75mm as per the above example.
Hope this helps and doesn't confuse you.
Cheers, Peter