No limits CNC

[Jasonb]

Yes Steve I know it can be done with a lot less I've done them myself even ones with just manual machines and mike Certainly does not have a fancy setup but it would be ideal for teh more rounded designs with thin tapering webs and fillets. I was thinking more that a small run could be done as there are many designs about that I'm sure people would make but don't due to the castings not being available, just look at something like the Motorboys plans books and you hardly see any of those being made. Same would go for the old Wall & Westbury designs

This is my Wall, crankcase two setups and each cutter changed manually (only got the one holder) Also base, manifold, flywheel, endplates, milled cylinder features, etc

[dieselpilot]

With Mach3 it was never necessary to home, and with soft limits the machine is protected.

This simply isn't the case. If the machine was configured to not require homing, you are taking a risk as to whether or not soft limits are within the machine's physical travels. Moving to X0.,Y0.(or any position) only helps if you have some physical reference you check. Linuxcnc stores the position on shut down. If the machine moves while the control is powered down the control has no idea where it is the next time it's powered up. This is where the risk is. If the machine hits a physical stop before the soft limit because the physical position and control position aren't aligned..... Forced homing prevents this issue.

  With a switch to PathPilot I need to reference each axis (i.e., click a button for each axis), but a configuration option lets this happen with no table motion.  However, referencing changes the values in the DRO.  For that reason, I shutdown the machine at the x0y0 position so that after referencing I can rezero the X and Y DROs.  I rarely leave a tool after shutdown, so the Z axis isn't an issue when referenced.  However, referencing Z sets its limit, so I'll typically jog it near to its upper limit before referencing.

The DRO changes depending on which work offset is active and how you're you're setting them. If the machine was homed when the work offset was set, homing again would not change the DRO for that offset. That is the function of work offsets. You can set one, and at any point later set the same values, and the machine goes to the same position.

No limit switch is provided for negative Z, but there's a rubber cushion at the bottom of the ball screw.

With homing and soft limits there is no need for hard limit switches when the control failure modes won't result in axis runaways. This machine design take that into account(hopefully).

[steamer]

The PCNC 440 does not have linear scales, or even motor encoders.  it only has limit switches, which is how it homes.   It counts stepper motor pulses and that is it.

Dave

[dieselpilot]

The PCNC 440 does not have linear scales, or even motor encoders.  it only has limit switches, which is how it homes.   It counts stepper motor pulses and that is it.

Dave

Yes.

[steamer]

And?

[stevehuckss396]

JasonB

I hear you. About 5 years ago I toyed with the idea of "electronic casting kits". You would get the basics in the form of Gcode and a setup guide for the block, heads, and oil pan and a set of drawings for the rest. If you had a machine run by Mach3 or compatible software you could simply setup your part exactly like the manual says and press cycle start and wait for the tool changes. I thought it would be a good way for hobbyist to make fancy things without buying fancy software or having fancy machines like that one. The crankcase on the engine in your photo would be a good example of what could have be done. It was not a well received idea so I forgot all about it. 

[Jasonb]

I was thinking more along the lines of the machined parts, at least the overall shape of major components  machined much like a casting but still leaving the builder the boring, turning and drilling to do. I other words a CNC machined "casting" set. Though an option at additional cost could be fully machined parts such as CNC cut cam profiles or finish machined castings.

I'm sure it would be a small market and maybe not worth the bother but if the CAD and CAM has been done then machining a second or six will be no more than the basic material and machining time and a bit of tool ware. A tool changer would help with reducing machining time or simply no need to stand around in front of the machine so you could be getting on with something else and getting a modest return from an otherwise unused machine. I expect farming it out to a small CNC shop would put the price to high but have no idea of their charges.

I you are aiming at those who already have a CNC then a step file of the assembly may be the better bet then they can access each part, decide how they want to machine it and run it trough their own CAM and Post processor to suit their machine and tooling complete with limits and stops as desired (keeping the thread on topic!). I did this with my Midget engine and the guy increased it back to the original size and has been machining the various bits on his own CNC.

[Hugh Currin]

Steve & Jason:

Alternately you could provide solid models and tool paths for the complex parts, such as the crank case. The purchaser would use their CAD/CAM program to produce the G-code, and/or make any modifications he wanted (feed speed etc). I'm thinking of Fusion 360 which has a minimal hobby package for free. If you sell the models you'd have to purchase a license for Fusion but that's not exorbitant.

It would probably take 10-12 hours before bootleg models apeard on the net though. Ya, not a great business model. But maybe something there for distributing model plans?

Just random thoughts.

[stevehuckss396]

Hello Hugh

Providing solids would be just a step above 2D plans. May as well just draw the part yourself from the plans.

[kvom]

Regardless of how they are set, I have the maximum X and Y motion +/- configured, and these are relative to the part x0y0.  These limits are large enough to cover 99% of parts I'd make and 100% of parts in the vise.

If I have a part mounted that might conceivably exceed a limit, I'll jog to the outer limit of the toolpaths as shown on the control.

[dieselpilot]

As we are all happy with the efficacy of our machines and practices, I have nothing else.

[Vixen]

What we are attempting to do is actually quite simply, it's to place the work on the table within the tables travel envelope.

There are many ways to do this, as we have read. Some methods use limit or home sensors, some do not.

There is no right way and no wrong way, as long as it works.

The discussion has been interesting and useful. Many methods have been described, We can now make our own minds up as to which way we want to go.

Thank you all

Mike