Messages

711

General Mach Discussion / Expected backlash

« on: January 21, 2013, 09:08:25 AM »

Hi folks, as a result of a slightly unexpected error in the dimensions of a piece I profiled I realised that I could not ignore the backlash on the slides of my little Novamill.  Measurement showed it to be 0.03 mm on X and Y, 0.02 mm on Z.  I have turned on compensation and set these parameters and it seems to work fine, but I was wondering what level of backlash was to be expected?  I have posted this question on the Denford forum and Angeltech has suggested I adjust the thrust bearings, which is good advice that I'll follow, as well as looking at the gibs, but would be nice to know what I could expect?  The machine though oldish has spent most of its life gathering dust in a school, having clearly not had anyone who had a clue in charge judging by the cutter jammed in a collet when I bought it off ebay!  So I don't think there will be significant wear.

John.

712

General Mach Discussion / Re: what pendant?

« on: December 31, 2012, 05:09:58 AM »

I started off with one of the Shuttle Express pendants originally designed for video editing, which does have a (sort of) MPG.  However I never found it very satisfactory, so now have an Xbox wireless controller.  This has only joysticks but I find it much better.  It would be nice to have an MPG tuned so that the wheel mimics the "feel" of manual drives but that seems not so easy to do.  The Xbox controller is cheap and I found installation very easy using the downloadable plugin.  The wireless is a delight, I was always getting the cable of the Shuttle would around me.

713

General Mach Discussion / Re: Myford Super 7 - adding ball screws

« on: December 22, 2012, 11:27:10 AM »

Well, I finally finished replacing my X-axis screw with a ballscrew.  I actually used one that I bought and had machined by John Stevenson to fit an X1 mill conversion I was doing, but them I bagged a Novamill on fleabay so the X1 got unconverted and sold!  The screw is a 5 mm pitch SKF, bought from Arc.  The main trick was to remove the nut (usual precautions) and re-fit the other way round so the cylindrical spigot points away from the lathe saddle.  (The problem here is that the original Super 7 L/S nut has a spigot 23 mm diameter that fits a bore in the saddle; with a flange to clamp on the saddle face.  The SKF nuts have a 24mm spigot.) Then I machined up a simple adapter plate which screws to the face using the original 4 BA bolts, and has 4 M4 tapped holes for the the ballnut.  A simple job on the CNC mill.  After fitting this everything went back together easily and the performance is much improved, it seems on an initial test to take off just what you tell it to, whereas with my previous plain screw it was very hit or miss.  If anyone is interested I'm happy to try to take some photos to show how I did it.  I will see how I get on with just converting the X slide, as fitting a ballscrew instead of the main leadscrew looks much harder.

John.

714

General Mach Discussion / Re: How do you Resume Cutting?

« on: December 18, 2012, 11:30:00 AM »

Another approach when you are learning is to use the single step feature which executes one block (line) at a time, each time you click Cycle Start.

715

General Mach Discussion / Re: Boxford AUD stepper sizes

« on: November 30, 2012, 04:24:09 AM »

I think the AUD is about the same size as the Myford 7?  I have used Nema 23 motors from Arc Eurotrade - I think 180 Ncm - and there is no sign that they lack torque for the job.  Will check exact type when I get back in the workshop.

716

General Mach Discussion / Re: Exporting tool offset tables?

« on: November 13, 2012, 12:33:41 PM »

excellent - thanks!

717

General Mach Discussion / Re: Exporting tool offset tables?

« on: November 13, 2012, 11:58:14 AM »

If I can get it out of Mach 3 that's a problem I can address!

718

General Mach Discussion / Exporting tool offset tables?

« on: November 13, 2012, 06:19:48 AM »

Slowly getting to grips with more advanced Mach 3 features and setting up tool offset tables.  Now I also need tool tables for my CAM program, for which I use G Simple (though I'm sure most CAM programs need tool tables.  Is there any easy way to export or copy the tool tables from Mach 3 to avoid having to re-type all the data, does anyone know please?

John.

719

General Mach Discussion / Re: Mouse interfacing

« on: September 23, 2012, 07:17:02 AM »

Thanks. 

720

General Mach Discussion / Re: Trying to understand thread wizard

« on: September 23, 2012, 07:10:57 AM »

I've also had lots of problems threading on my CNC converted Super 7.  Much of the problem seemed to be down to accurately knowing the tool tip radius, I haven't returned to try again yet but have got a microscope set up so I can measure it now.

Also had big problems with backlash compensation on the lathe.  The documentation on it is poor, but it does say somewhere (can't remember where) that it doesn't work for programmed moves that are smaller than the backlash.  For a lathe without ballscrews that's a big problem since the BL on the main leadscrew can be quite large - for example on mine, which is relatvely unused and unworn, there is 0.25 mm on the Z axis.  So for example, if you want to zero the tool on a faced end of the stock, then back the tool towards the headstock and turn towards the faced end, you can't rely on the backlash compensation to correct it AFAICS.  You could imagine building backlash into the G Code, so wizards for example account for measured backlash when planning moves, but this sounds a lot of work and would rule out using third-party G Code.  I am biting the bullet on this and working out how to fit ballscrews on each axis!

John.