Manual Numerical Control - 'CNC' done by hand with a DRO

[silverfox]

I dont mind sucking a lightbulb!

[Roger]

This thread was started with the intention of exploring the single topic of using G-Code generated from CAD/CAM systems with a DRO. With this method, the DRO is simply the way you can see where you are, nothing more than that. No special functions are used and the datum is set only once. I think there has been some misunderstanding that this is in some way a difficult or advanced use of DROs, whereas the opposite is the case.

DROs are wonderful things in their own right. Most come with clever functions which can greatly assist in creating patterns of holes or arcs. I'm not suggesting that these things are not useful or that some of the things I've described can't be done in other ways.

The specific point I'm trying to make is that you can model a part and guide the software to generate useful lists of coordinates. That's all. This method doesn't require you to know anything about DRO functions other than how to set the zero position once for the whole set of machining operations on that face. That might be all of the fixing holes and ports for a cylinder block for example. You don't need to move the zero point from feature to feature, the CAM software knows where the zero is and outputs everything relative to that.

I've asked the Administrator to change the title of the thread to be more specific since it appears to have caused some confusion.

I think it's a good idea to start a new thread that explores the different functions of DROs and how to use them more conventionally.

[simplyloco]

That's a good idea Roger. I have to admit that your earlier posts gave me the impression that the CAM co-ordinates could be output to the DRO, but I think ?  now that one would set the zero manually and work to co-ordinates on a printed program list. Or have I still got it wrong?!
John

[Roger]

Sept 4, 2018 9:19:11 GMT simplyloco said:

That's a good idea Roger. I have to admit that your earlier posts gave me the impression that the CAM co-ordinates could be output to the DRO, but I think ?  now that one would set the zero manually and work to co-ordinates on a printed program list. Or have I still got it wrong?!
John

Hi John,
The DRO is just used to show the position the table moves to when you wind the handles. There's no connection between the computer and the DRO. The idea is that you wind the handles to the positions show in the list, that's all.

So yes, you have the right idea. It looks complicated at first glance, but actually it's a simple idea, just not an obvious one.

[Neale]

I used this technique a few months ago to turn the flange profiles on a set of 5" Black Five tender wheels. I was scratching my head wondering about form tools and so on, then realised that if this were a CNC milling/routing operation, the answer would be trivial. So, off to PC, draw flange/tread profile in F360, then "pretend" to mill it with a 5mm dia cutter, which happens to be the size of my small carbide button lathe tool. Throw it at the CAM module, extract gcode, quick hack with a text editor and I ended up with a printed list of XY (well, XZ when transferred to lathe) coordinate pairs to use with the DRO. I was pleasantly surprised how quickly I could run through the list of coordinates, and probably saved a lot of time compared with trying to make a form tool. Maybe not the way to go if you are mass-producing but for a few off, it worked for me. I'm about to machine the buffers and will use the same technique to machine the front and edge radii. I hate having to do anything by hand that I can get a machine to do for me!

As has been said already, a DRO might have suitable functions for holes on a line at an angle, chain drilling circular arcs, and things like that, but for irregular shapes that the DRO can't handle, the CAD/CAM approach has a lot going for it.

[Roger]

Oct 12, 2018 22:06:19 GMT Neale said:

I used this technique a few months ago to turn the flange profiles on a set of 5" Black Five tender wheels. I was scratching my head wondering about form tools and so on, then realised that if this were a CNC milling/routing operation, the answer would be trivial. So, off to PC, draw flange/tread profile in F360, then "pretend" to mill it with a 5mm dia cutter, which happens to be the size of my small carbide button lathe tool. Throw it at the CAM module, extract gcode, quick hack with a text editor and I ended up with a printed list of XY (well, XZ when transferred to lathe) coordinate pairs to use with the DRO. I was pleasantly surprised how quickly I could run through the list of coordinates, and probably saved a lot of time compared with trying to make a form tool. Maybe not the way to go if you are mass-producing but for a few off, it worked for me. I'm about to machine the buffers and will use the same technique to machine the front and edge radii. I hate having to do anything by hand that I can get a machine to do for me!

As has been said already, a DRO might have suitable functions for holes on a line at an angle, chain drilling circular arcs, and things like that, but for irregular shapes that the DRO can't handle, the CAD/CAM approach has a lot going for it.

A variation on this for higher volumes is to use the exact same technique but use it to create a form tool which can then be used for all of the others.

I've got a 3D model that I use for making these. The idea is that the profile you machine is modified so that the form tool can be machined while tilted up at the front clearance angle but it's used flat to create the profile I actually want. You can get away without top rake on form tools.

It took a bit of head scratching to get the model right, but now I can just draw whatever shape I want on the appropriate plane in the model and then project that onto the X/Y cutting plane for the CAM output.

[Neale]

Roger - that sounds like an interesting approach. I'm a member of a small team that recently built a wire spark eroder (it's been demonstrated at a few of the ME shows over the last 18 months or so) and I have experimented with cutting a tool directly in an HSS blank. I actually made a 47.5deg BA screwcutting tool, with a tiny triangular tip right on the edge of the blank to allow screwcutting as close to a shoulder as possible, but the technique would work for any profile. The machine is with a colleague from the team at the moment, but it's something that I want to explore further when it gets back to me. I cheated and just tipped the tool up at 5deg or so to provide front clearance but I take your point that you should modify the profile slightly to allow for cutting out of the plane of the tool itself. Fortunately, things like Fusion 360 do make this kind of thing straightforward and avoid the need for pages of trigonometric calculations! Cutting with the equivalent of a 12thou cutter also helps with the detail...

[Roger]

Nov 6, 2018 14:57:06 GMT Neale said:

Roger - that sounds like an interesting approach. I'm a member of a small team that recently built a wire spark eroder (it's been demonstrated at a few of the ME shows over the last 18 months or so) and I have experimented with cutting a tool directly in an HSS blank. I actually made a 47.5deg BA screwcutting tool, with a tiny triangular tip right on the edge of the blank to allow screwcutting as close to a shoulder as possible, but the technique would work for any profile. The machine is with a colleague from the team at the moment, but it's something that I want to explore further when it gets back to me. I cheated and just tipped the tool up at 5deg or so to provide front clearance but I take your point that you should modify the profile slightly to allow for cutting out of the plane of the tool itself. Fortunately, things like Fusion 360 do make this kind of thing straightforward and avoid the need for pages of trigonometric calculations! Cutting with the equivalent of a 12thou cutter also helps with the detail...

Hi Neale,
That's a very useful piece of kit. I have to make to with tiny cutters on the mill if it needs to be really fine. I can go down to 0.5mm which is not far off your 12thou, but there's no way I could machine HSS. Gauge plate is my choice of material.
I didn't mention before, but I made a wedge at the 5 degree angle to rest the stock at the right angle in the vice without having to measure it. Simple ideas like that are a real time saver and you only have to do them once.