Some basic questions for the experts

[jdell42]

Ok.. I have been digesting all the info on this site for the last week. I stumbled across this site and can't believe a CNC router is both within my price range and capabilities. This site is incredible.

Needless to say I have a few lingering questions on some things that are fairly basic.

1. Clamping the parts
This is pretty obvious but if you are cutting to the full limits of the machines capacity this may get tricky. Is a common approach to put stops in the programming to move clamps around etc? Do most put the aluminum T Track in their router beds to aid in clamping? I would guess its probably best to not move clamps around such that the work is not accidentally moved so I was wondering how the pro's do this.

2. Bit / Mill Changes
Again.. another common task I have not gotten my head around. Everything is clear except the z-axis. How do you "re-calibrate" new z-axis relative to the work for the new bit height? Do you use a limit switch or some other method for this? I am assuming you can change a bit without messing up the x&y axis but not sure about that either.

3. Router Speed Control
Is the router wired to into the power supply / controller such that it starts & stops via the CAM software, or is it simply turned on and the speed is set manually? I am assuming you can do this both ways but do some of the more common controllers ie Hobby CNC have these features?

4. Bits Types
What type of bits are used for cutting MDF & plywood vs Aluminum. Not sure if I plan on cutting an aluminum but it would be good to know.

5. Cutting through the material
Ok.. if you want to completely cut through a piece of material how do you do this without cutting your router bed up? Is the router bed a sacrificial part meant to be replaced? or are these machines that accurate? When cutting on a mill I have seen precision blocks used.. but not sure how this is done with a large piece of wood.

Thanks,

John

[HuFlungDung]

Shucks, those aren't questions for the experts, they're for the newbie

RE 1: Clamping can be a tricky issue at times. You can pause your program and move a clamp. Do not release them all at once and the part should stay put, providing you use at least 3.

Many guys doing router work will attempt to hold the material down with a vacuum ported table, or whatever, in order to avoid the nuisance of edge clamps.

RE 2: Differing tool lengths is a common concern with multi-tool programs. Nearly every machine control in existence uses a tool length offset register (chart) in the control, which contains a measurement that the user determines is the difference in length between the master tool (Tool1) and each subsequent tool. This measurement is automatically applied when a tool is loaded, and the relevant tool offset is recalled from the offset register.

RE 3: If the spindle motor is variable speed, and has a drive amplifier capable of receiving input from the controlling software, then the motor can be run at user specified rpm. For the hobbyist, this may be an unnecessary expense, and he could simply use some sort of manually operated speed control. A pause can be inserted into each program, after a tool change, to allow the user to adjust the speed before continuing with the execution of the program.

[paulC]

4. Bit used is dependant on many things. Ply and MDf can be cut with any router bit. MDF is quite abrasive and Carbide will last longer. Aluminium I would only use carbide. The secrets to cutting aluminium with a router are:
Don't cut more than 0.5mm per pass.
Slow feed. I run mostly 150mm/minute.
Clear the chips. As soon as you start recutting chips the aluminium will melt to the cutter and things will go bad. I use compressed air to clear the chips.

5. You don't want to cut your table. Use a spoil board. This can cover the whole table or just the area under the work piece.

Paul

[drawbar]

RE2: I use a Dremel Advantage on my router, and when I insert a new bit, it never goes back to the same spot it was before in the collet. So what I do is jog the bit down close above my 'zero' surface (usually the top of what I'm cutting into). I slip a piece of paper under the tip of the bit, and jog down incrementally, 0.001" at a time until the paper just begins to grab between the bit and the material. I then set the Z axis to 0.004". That's always close enough for what I do.

Brian

[spalm]

We are talking hobby level here, right? I am somewhat repeating what others have posted, but hey...

RE 2: Before you start to route, lower the bit by jogging until the bit just barely touches the top of the work piece and the X-Y is where you want to start the cutting. Zero out the 3 X-Y-Z positions in the control software (Mach3 etc.) Route away. To change bits, turn off the router but not the stepper motors, so there is no slippage of the XY axis. Manually jog the router over to where you can easily change bits. Now tell the software to go back to X-Y 0-0 (Home). Lower the new bit until it just touches the top of the work piece and again zero out the Z. Raise the bit and start the next pass. (I use a macro in Mach3 that automatically lowers the bit until it touches a “touch plate” that I momentarily place on the work piece. It then zeros the Z and raises the bit to a safe distance.)

RE 3: Use a router with a built in speed control.

RE 4: Standard carbide router bits are fine. You will want a few types. Spiral cuts are great for cutting things out, while V bits and round bottom bits are used for cuts that don’t go all the way through.

RE 1 & 5: Use a spoil board clamped to the top of the machine. Double sticky tape works wonders for small parts and helps hold larger pieces from shifting while moving clamps around. Several CAM programs will let you route everything except some small thin tabs that will keep the cut out part connected to the original board. Therefore you only need to clamp the board at the edges and you can sand these off later.

Steve

[dertsap]

for me ,a couple spots from the glue gun works great for holding the part to the table

[jdell42]

Thanks everyone. Looking at the answers everything seems pretty simple now.

One follow up on the router control. Do people typically wire this through a controller board/software/limit switch such that if an emergency stop or limit is hit it shuts down?

-or- is the basic setup simply a variable speed PC router plugged into the wall and turned on/off and speed set manually?

[spalm]

I would bet that the second case is the norm, but the first case is what we all want but never had the time and money to install/build. There seems a never ending list of things we want, but sometime you just got’a just build it and go.

Steve