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Author Topic: Front & rear toolpost in Turn 42.020  (Read 8027 times)

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Front & rear toolpost in Turn 42.020
« on: January 29, 2009, 03:38:25 PM »
Folks,

I'm trying to set up my little lathe with a toolplate (at least that's what I gather it is called) meaning I've got several tools all fixed on the same plate. I would like to use a front and a rear toolpost. Now I've tried to use the "front" and "rear" setting in the tool table but I don't quite get what it does. What I'm looking for is a way to set things up so mach "knows" that for example tool 1 is mounted on the rear toolpost and so moves the X-axis backwards for larger diameters. Same way for tool 2 being in the front toolpost having to move forwards for larger diameters. Now I know that in G-code I could use negative x-values for reartoolpost and positve for front but that seems a bit of a roundabout way of doing things particularily if I'm using a CAM software.
I've read Hood referring to issues with the front and rear setting in the tool table, is there anybody with more input on this?
Another question: what does "Direction" in the tool table do?
Greets Dave
« Last Edit: January 29, 2009, 03:43:27 PM by acieradave »

Offline Hood

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Re: Front & rear toolpost in Turn 42.020
« Reply #1 on: January 29, 2009, 04:08:01 PM »
Dont even attempt to use front or rear at the moment its never worked right and will just cause you hours of frustration and broken tools. Use one or the other and stick to it. Brian will be working on it at some point, supposed to be in a month  but..... well we all know that some things can take longer and looks like the comp and open GL that he is doing first is going to take a while.
 The way I work things at the moment is either put -ve numbers like you say or most of the time I just code all positive and if using a boring tool on the front post (rear turret is my default) I just have a G51X-2 in the code  before the tool is used (-2 because I am in Dia mode, if in Rad then -1) when I have finished with that tool and am going back to the rear turret a G50 will cancel the scale.
Its a real PITA to have to do it but at the moment its the easiest.
Hood
Re: Front & rear toolpost in Turn 42.020
« Reply #2 on: August 27, 2009, 07:25:10 AM »
Hi Hood,

I have just finished building my own designed lathe and now the battle begins.

Currently I am using a front toolpost.

I used Mach 3 turn wizards to generate G code for a 24.5mm ball.  I hand edited the code to add such things as CSS.  The air cuts work fine except that the the X cuts are on the positive side of centreline rather than negative.  I tried your trick of using G51 X-2 in diameter mode but my code simply ignores the intended result, that is, cut on the negative side of centreline.

Can you have a look at my code to see where I have gone wrong?

Regards

Chrisjh
Brisbane Australia

Offline Hood

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Re: Front & rear toolpost in Turn 42.020
« Reply #3 on: August 27, 2009, 08:50:21 AM »
If you only have either a front or a rear post and not both then there is no need to do the scale factor.
 Your problem is two fold, firstly it is G51 not G52 and the main reason you will be needing to use it is I think you must have the setting for "Show tool above centreline in Turn" chosen. For a front post lathe you dont want that. You will get it from Config menu then down to ToolPath.

If you still have problems attach your xml and I will have a look.

Hood

Offline Dan13

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Re: Front & rear toolpost in Turn 42.020
« Reply #4 on: August 27, 2009, 01:57:58 PM »
Sorry for interrupting the discussion, but I don't think I understand Hood why you need the scale factor if you change from a rear tool post to a front one? Are you changing the direction of rotation of your spindle and you need to change the X values from negative to positive?

And why by a factor of (-2) and not (-1)? If you're in dia mode and have for instance X-10, wouldn't G52 X-1 convert it to X10?

Daniel

Offline Hood

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Re: Front & rear toolpost in Turn 42.020
« Reply #5 on: August 27, 2009, 02:04:18 PM »
My code is written as if the tools are all on the rear turret , the front post doesnt come much past centre. I could manually change all of the X values to negative values but much easier just putting a G51X-2 in once :)

 I am in Dia mode but scaling doesnt seem to know that ;)

Hood
Re: Front & rear toolpost in Turn 42.020
« Reply #6 on: August 27, 2009, 09:15:19 PM »
Thanks Hood for checking my code.

My dyslexia kicked in once more.  I typed G52 X-2 instead of G51 X-2. >:D

After correcting my error, the code then wanted to cut all around the full circumference of the ball. ???

My lathe is actually designed to take gang or tool plate tooling so I thought "What if I pretend to use a real toolpost when in fact I have the tool mounted in a front toolpost like Hood does?"

I set the tool table to tell Mach3 that the tool was mounted in a rear toolpost and voila, it worked!!!  ;D

I am now one step closer to actually cutting metal (Still trying to build up the confidence and courage). :-[

Attached is a photo of my home designed and manufactured lathe.

Basic Specs:

Spindle Bore 38mm with D1-4 chuck interface. (I purchased a spare spindle for my manual Chinese lathe and used it rather than make one from scratch.  I couldn't make one for the price of the spare part - $260AUD).

Danfoss VFD controlled through PWM in Mach3 with my own PWM to Analogue Converter with OPB960 through 8mm Slot Index Pulse generator mounted on the Spindle (CSS works flawlessly).

.75KW 3 Phase motor with approx 3:1 Pulley Ratio and Powertwist belt.

Smooth Stepper

Hywin Linear Rails and Linear Bearings and 5mm pitch ball screws and nuts.

Leadshine M542 Stepper Controllers with 430oz/in Z Stepper and 311oz/in X Stepper.

My own bearing housings with Dual Row Angular bearings where it counts.

12months of research and design and a lot of blood sweat and tears inc lots of good Aussie dollars.

Hopefully I can post a video soon.

Kind Regards and once again, Thanks.

Chris Humphris

 

Offline Hood

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Re: Front & rear toolpost in Turn 42.020
« Reply #7 on: August 27, 2009, 09:23:51 PM »
Very nice looking lathe :) What is the bed made from?
 Look forward to seeing it running and I know how you feel, I still get nervous sometimes seeing the 400KG saddle moving at 10m/min towards the chuck ;D

Hood
Re: Front & rear toolpost in Turn 42.020
« Reply #8 on: August 27, 2009, 10:04:09 PM »
Hi Hood,

The bed is 200 x 75 C Section steel.  It is only 6mm thick across the wide part so as a precaution I have added a 16mm thick steel plate under the headstock end to ensure that all is stiff.

I had to machine the linear rail and headstock contact faces in one set to ensure that everything was in the same plane.

The bed is 1m long (too long for my manual mill so I had to get it machined by some blokes I know who have a HAAS VF5 with extended bed.  That machine is huge. See Photos.

Everything else I machined myself using my manual lathe and Mill + my Syil X3 cnc mill.

Regards

Chris

Offline RICH

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Re: Front & rear toolpost in Turn 42.020
« Reply #9 on: August 28, 2009, 10:21:19 AM »
Chris,
Nice going on the lathe. Let us know how it works out and if you know of anything you would have done differently.
I was going to do similar as i had some heavy duty rails but decided to convert my mint 6" Atlas instead. Like you would have had to get the mounting plate machined and a machining resource has since retired and sold out the shop ( had one of the biggest Haus mills around).

OH, just for Hood, I aligned the guys other mill , made by Cinncinnati Machine, it had a 40' long x 5' foot high bed and the counter weight for the Z head was 10 tons. He used to verticaly machine 6'x6'x 4" thick AL plates prior to having them ground. The 2' thick reinforced pad that it sat on used to move overnight and drove me crazy for a few days. Wish I took some pictures.
RICH