[Richster]

Very nice machine build. Very clean looking wiring management also.
CarveOne

Thanks Yes I pondered long and hard about how to route the cables best, since I wasn't so keen personally on the proposed way in the plans. I'm pleased with how it worked out in the end. There is also the issue that all my cables are right next to each other in the cable runs, but with the opto-coupling in place this doesn't seem to be a problem. The other thing I've done is soldered all the stepper connections in an attempt to protect the driver board. There's always the possibility that a wire will break over time through fatigue, but I hope the mic cable I've used will be fairly immune to this.

Couldn't resist the final HDPE mount, so here goes:

Cutting the mount...


Old and new


Fitted - much better! This one gives me a little more adjustment too, which is a bonus.

[thkoutsidthebox]

This is turning out to be a great build. Certainly much more professional than my solsylva build. Well done.

[Richster]

I shelled out on a Mach3 license this week, so that's opened up a whole new world of machining opportunities. Next up I can see myself getting the LazyCam license (unless anyone knows of any cheap alternatives)? All the really useful features are disabled in the demo version

First up some plane parts, actually not for me this time since I possibly have enough models already?


And secondly, a not particularly successful dinosaur model.


This isn't complete BTW, there's plenty more pieces!

I need to re-make this with a smaller cutter and thinner material ideally. Although it came from the dino thread on this site, I am not quite sure which it is (I think it's a Triceratops), and more importantly, I'm not completely sure how it goes together! If there's a photo lurking anywhere of this particular model, I'd love to see it! I couldn't find one....

**edit** this looks remarkably similar...
http://www.shop4-toys.com/images/saf730210.jpg

[Richster]

Having found some great free software, I've finally got round to posting a wiring diagram for my machine, which is hopefully of use to some of you. I've put it in what I hope is the 'correct' forum:
http://www.cnczone.com/forums/showthread.php?p=473239

[thkoutsidthebox]

Did I mention I have a LazyCam license, but I bought it by accident when I intended to buy the NewFangled Solutions license and have never used it.....

[Richster]

This evening I gave in and made an additional router clamp. Having had some use out of the machine, I was starting to get a little front-back flex on the router since it was only attached at the base. This modification makes it rock solid.


To make this I took the router apart (the main case splits into two just above the brushes) and got a graphic of the outline via my flatbed scanner. It was then just a case of drawing an outline in AutoCAD, then getting the rather wonderful Cut2D from Vectric to do the rest. The fit's not perfect, but it's certainly tight, so works really well These components are made from my now somewhat diminished stock of 10mm HDPE.

Here's what I got from the scanner...


One side-effect which I wasn't expecting is the machine now runs a little quieter! I imagine the HDPE is absorbing some of the vibrations from the router which would otherwise be transmitted through the machine. Whatever the cause, I'm certainly not complaining!

[Richster]

Just ordered me a stepper motor damper from here:
http://www.rino.co.uk/products.asp?recnumber=1232

Will try it out on the Z-axis and see if it improves things. Might be worth a shot on the Y and X too - I'll try it out.

There's a 3-week lead time on this, so watch this space!

[BillTodd]

Just ordered me a stepper motor damper from here:
http://www.rino.co.uk/products.asp?recnumber=1232

Will try it out on the Z-axis and see if it improves things. Might be worth a shot on the Y and X too - I'll try it out.

There's a 3-week lead time on this, so watch this space!

Richster,

How is the Z axis motor coupled to the lead screw? (I'm just surprised you need to add to the rotating mass)

Sorry, if I'm teaching granny to suck eggs but, you might be better off with a compliant coupling between motor and lead screw.

On my small homebrew engraver I initially used rigid oldham couplings, which caused all sorts of problems. I solved these by using a soft rubber tube, stiffened with a split plastic tube over the top. (see attached).

[Richster]

I have the fuel tube couplings as per the plans. The issue I have is a resonance problem, i.e. there is a range of speeds where this axis will stall. Above this speed (where there is actually less torque available) it runs OK. It was suggested by others on the forum that the damper can sort things out on a Xylotex system. It wasn't hugely expensive in the big scheme of things, so let's see...

[BillTodd]

I have the fuel tube couplings as per the plans.

Are they stiff enough?

Steppers are a real PITA sometimes!

[Richster]

I don't really have the experience to compare them with anything. I guess there's a tiny bit of twist in the link, but given that a whole turn gives just over 1mm movement, it's not enough to keep me awake at night. More the issue is the backlash which is inherent in the cheap leadnuts.

[BillTodd]

I don't really have the experience to compare them with anything. I guess there's a tiny bit of twist in the link,

I'm just wondering; There will always be some frequency at which the springyness of the joint, coupled with the mass of the lead screw will resonate. If there's too much 'give' in the couplings, this resonance will be at a lower frequency than the maximimum speed (which is what I think you're seeing). While you're waiting for the dampers (which will probably solve the issue by changing the resonant frequency anyway), how about trying to stiffen the rubber tube by doubling it up ?

More the issue is the backlash which is inherent in the cheap leadnuts.

I solved that by making my own out of PTFE (see pic - The brass adjuster is actually unnecessary, since the PTFE stretches a little as it is tapped, the resultant thread is quite snug).

[edit] P.S. if you need a bit of PTFE to try, send me a PM


[edit2]

Just thought of something you could try:

If you leave the motor connected to the driver but switch the driver power off (or disconnect the motor and short its wires together), you should be able to feel the motor 'cogging' or stepping as you turn it.

If you turn the motor with the lead screw, you should be able the feel the lead screw give a little before the motor jumps to the next position (if there's no give the coupler is too stiff). If the the motor jumps more than one step as it catches-up with the lead screw, then the coupling is too soft.

[Richster]

Thanks for the further thoughts there.

In terms of making the PTFE version, I guess all I need is the appropriate size rod (the existing leanuts are 13mm across the flats from memory) and tap the center M8, ideally using a lathe to center the hole? I don't think the rod is available in this diameter but I guess I could turn down an oversized one? Then it should fit in my existing components OK without changing anything. I imagine I don't want to go too tight on the threads or the steppers might stall at the higher speeds.

Do you have any views on mounting it like my existing leadnuts i.e. a couple of M4 machine screws into the side?

Thanks for the offer of the sample - I'll probably buy some at some point to be honest, it's not particularly expensive.

Cheers - Rich

I'm just wondering; There will always be some frequency at which the springyness of the joint, coupled with the mass of the lead screw will resonate. If there's too much 'give' in the couplings, this resonance will be at a lower frequency than the maximimum speed (which is what I think you're seeing). While you're waiting for the dampers (which will probably solve the issue by changing the resonant frequency anyway), how about trying to stiffen the rubber tube by doubling it up ?



I solved that by making my own out of PTFE (see pic - The brass adjuster is actually unnecessary, since the PTFE stretches a little as it is tapped, the resultant thread is quite snug).

[edit] P.S. if you need a bit of PTFE to try, send me a PM


[edit2]

Just thought of something you could try:

If you leave the motor connected to the driver but switch the driver power off (or disconnect the motor and short its wires together), you should be able to feel the motor 'cogging' or stepping as you turn it.

If you turn the motor with the lead screw, you should be able the feel the lead screw give a little before the motor jumps to the next position (if there's no give the coupler is too stiff). If the the motor jumps more than one step as it catches-up with the lead screw, then the coupling is too soft.

[flyboy1015]

Rich,

That's a very nice build. I also have a dual lead screw solsylva, but it's not nearly as nice as yours. Very impressive. I can see that you've put a lot of thought into it. Thanks for sharing. Mine has been sitting on saw horses for the better part of a year. I think I'll make stiffeners like yours to mount to the underside of my table. I have a need for some portability, but haven't come up with a suitable solution. I think I've just found the solution that I like.

Chad

[ambrosefx]

Try Alibre, They have a free express version of Alibre CAD and Alibre CAM I think tha WWW is http://alibre.com

Bryan

[BillTodd]

I imagine I don't want to go too tight on the threads or the steppers might stall at the higher speeds.

Yes, but it's slippery stuff I can easily get ~5000steps/sec (400 half-steps/rev) with a fairly heavy and stiff X axis.

Do you have any views on mounting it like my existing leadnuts i.e. a couple of M4 machine screws into the side?

I doubt you'd get a fixing like that in PTFE that would be stong enough with a couple of M4s. Although, if you could off-set the drive thread to one side so you could get an 8-10mm deep fixing thread, it might do the job. You could always add another fixing screw.

[Richster]

Hey I recognise that black-ash desk!

Thanks for the further info, will have a think about a possible different approach for the mounting...

[AngelT]

Instead of using a fuel line as a coupler, I used a 1/4 metal coupler drilled to 5/16 on one end half way through...To hold the router I machined from PVC the holders....Intend to replace the trimmer router form Harbor Freight, it is a cheap one if you know what I mean...sometime have to bang the body in order to run. I guess the clamps are distorting the body and the brushes are not making good contact. Next one will have a metal case.

[Richster]

A quick update - particularly as I'm long overdue a post.

I had a meeting with a tree and a new-ish aeroplane a few weeks back - a new wing was going to set me back about £90, so what with the world being in it's current crisis I have knocked up a new one on the machine. This type of wing, which tapers across it's span, is quite hare to make by 'traditional' methods. Also, the spacing between the ribs varies, adding to the difficulties.

So....

I scanned the root and tip rip into autocad, then plotted the appropriate airfoil (this one is symmetrical). Autocad then did the work calculating the intermediate ribs by scaling them to fit the space. The CNC also did the work cutting out the webs, which are the vertical panels between the ribs, ensuring that everything lines up and that the LHS and RHS are mirror-image copies of each other. So what I have is more or less an exact copy of the commercial wing (shh don't tell) for a fraction of the cost. Using a 800W router to cut balsa is a little like using a sledgehammer to crack a nut, but better overpowered than under I guess. Here she is:


On other things I'm still waiting on my vibration damper to turn up (long overdue), but other than that the machine remains unchanged since previous posts.

[thkoutsidthebox]

Niceeeeeee wing.