Newbie- Z Axis stalling when plunging slot drill

[Adethelathe]

Hi there.
I am a newbie to this group so forgive me if I don't use the "normal" protocol.

I have recently converted an old U.K.Elliot (Linley U.S.) mini jig borer to CNC and am very pleased with its performance apart from one area which I will detail below.

I am using TurboCad/Cam and Mach 3.

All axis are driven by stepper motors and the machine has accuratly produced a range of items from 1.5 x 3 mm brass componets right up to 4 mild steel locomotive coupling rods just under 8 inches in length and 0.375 thick.

The problem I am having occurs when I try to plunge a slot drill into mild steel or even brass when making a pocket. The Z axis stepper motor intermittantly stalls. I have tried different feed rates and spindle speeds with no sucess. I have also tried different motor settings on Mach 3 motor tuning.

The stepper motor is directly coupled to the quill feed in place of the original handwheel. The quill uses a helical gear to produce the vertical movement.

Is it that the srepper motor I am using has insuffient power?

Things I have considred, but am not sure about:
* Should I try a reduction gear to produce more torque before going for a more powerful motor.

* Would "pecking" when plunging be a solution, though TurboCam wont let me using pecking with a mill. I would have to insert the G code manually.

I am sure someone must have had a similar problem to this and I am keen to hear from anyone who can help.

Adrian

[Kipper]

A quickie...How many steps per unit and what microstepping and what "effort" does it take to turn the handle manually for the same feed... Also how powerful are the drivers and motors......Not much to ask eh?

[Adethelathe]

Hi Kipper

Thanks for your response.

Some answers to your questions.
The stepper motor has a holding torque of 1.85Nm. , degree/step = 1.8.

I have set the driver to 1600 microsteps/motor rev. Peak current is set to 2.52Amp, and the power supply is 24 Volts.

The steps per unit is 16 per 0.001", so Mach 3 is set to: steps/per motor rev 16,000. 1 revoultion of the old handwheel = 0.1"

I can't recall any problem with effort using the old handwheel, but will fit a handle of a set length say 6 or 12 inches to get an idea of the effort to plunge a 3/8 slot drill.

By the way what part of London are you in? I live near St Albans.

Regards

Adrian

[Kipper]

Ah so 1/8th microstepping and....I have no idea what those 0.001" things are...How many steps to get a unit ie 1" then I can convert it in my head to the modern Metric system.

24V is a low voltage.....what driver is it and what max voltage can it use.

On a second look it seems to be a 1:1 connection from the stepper to the quill or some other....is this so?

Not in London matey.... Leeds...Up north where we all have flat caps and say "thee an thy"

[Adethelathe]

Hi Kipper

Sorry about the 0.001. I can use both imperial and metric, though my age of 57 I tend to go for imperial. 0.001 is 1 thousend of an inch , so for 1 inch or 25.4 mm there are 1000 x 0.001.
The drive as you say is 1:1

The max voltage for the driver is 32, but the recomended Voltage is 24. This si supplied by Motion control in Bournemouth and is a MSD325

Seem to be getting somewhere having fitted the handle. This was 8" (203mm) piece of 3/8 (9.5mm) square steel. I attached this to the rear end of the stepper motor shaft and it moved the quill down under its own weight. No effort plunging a 9.5mm slot drill, untill I felt a lot of resistance. I am thinking there might be a bit of swarf in the helix, so am stripping that down next.

I am very interested in knoiwing if I have got the correct settings for the stepper motor. What is the trade off of the number of steps against torque. I would be happy with a Z Axis accuracy of 0.001" (0.0.254mm) if I can have greater torque.

Regards

Adrian

ps Dont know why I thought you lived in London.

[Kipper]

For details on the workings and ratings of stepper drives/motors I'd just point to the Geckodrive website's FAQ section......

The rating of 24V is the "typical" Voltage supply....there's some cheap 30V regulated one's on ebay at the moment. here interestingly they are adjustable within a 10% range! with 8A total available current it seems a match made in....machine heaven

I have no knowledge of your particular machine so can't say what ratio speed v torque would be best.... My Z moves at 800mm/min max (31.5" in old money) and is just fine for my usage.

Any pictures of your machine and it's drive to the quill?

[Adethelathe]

Hi Kipper

There was some swarf in the vertical lead screw that linked to the helical gears. I have tried milling some brass and no problems at all. I will try something harder tomorrow.

Mnay thanks agaian for the suggestion of a handle. this led to finding what could be the main problem.

I can and will adjust my power supply and take it up to 30 Volts.

I will also look at the Gekko web site you suggested.

You can see what my mill looks like at the following site.

http://www.lathes.co.uk/elliott%20mini%20jig/index.html

Will let you know how I get on tomorrow and what I find at the Gekko site.

REgards

Adrian

[Kipper]

It's cute! I have the same machine lamp on my lathe

You'll be jigging around in no time

[John Welden]

* Would "pecking" when plunging be a solution, though TurboCam wont let me using pecking with a mill. I would have to insert the G code manually.

Program a peck drilling cycle with the same tool number that you're using for the endmill.

I'm just giving a programming work around, I have no idea if it would help with your stalling problem.