Tapping aluminum plates

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Caesar S
Posts: 197
Joined: Mon Sep 29, 2014 7:19 pm
Location: Seattle, WA

Tapping aluminum plates

Post by Caesar S » Wed Feb 11, 2015 7:59 pm

We currently tap 9x9 inch aluminum plates manually (drill press with Procunier attachment). It's very tedious as the plate has to be repositioned for each tap. There are approx 40 holes to tap.

ShapeOko 2 would be ideal for this task. Has anybody converted their spindle for this? The Procunier attachment is about 6 inches tall and weighs 4 lbs.

Are there alternative to the Procunier attachment?

At the heart of it, I'm thinking of using the Z screw hard coupled to a tap. However matching the depth per rotation to the tpi of the tap seems complicated.

Any ideas? We really don't want to buy a lathe to do this (plus a rectangle is difficult to attach to a lathe's spindle).

Caesar S
Posts: 197
Joined: Mon Sep 29, 2014 7:19 pm
Location: Seattle, WA

Re: Tapping aluminum plates

Post by Caesar S » Wed Feb 11, 2015 8:21 pm

Another approach is to use a stepper motor as the spindle. The tap would be attached to the spindle.

This way the tpi is set by the number of rotations of the stepper motor.

It would need electronics to drive the stepper motor closed coupled with the z stepper motor rotation.

I could use an Arduino to sense the z motor pulses along with time as inputs to calculate the spindle stepper rotation.

Ughhhh, I'd rather pay somebody who already has this solution.

Hans
Posts: 290
Joined: Tue Dec 25, 2012 5:19 am
Location: Connecticut, USA

Re: Tapping aluminum plates

Post by Hans » Wed Feb 11, 2015 9:05 pm

I think the simplest way to synchronize tapping with a stepper as a spindle like you suggest would be to use a tinyG or Mach3 and program the spindle motion as the C axis. I would write off thread milling because a Shapeoko won't hold tight enough tolerances. Rigid tapping might work, and you may as well try it and see if you break a tap before you try to rig up the Procunier. What size holes are you tapping? Tapping takes a lot more torque than a Shapeoko is made for, and as a total guess I don't see a Shapeoko holding up to even 1/4-20 in metals.
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RobCee
Posts: 587
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Location: Birmingham, UK

Re: Tapping aluminum plates

Post by RobCee » Wed Feb 11, 2015 9:08 pm

I would think that the torque required for tapping might be more than the ShapeOko could withstand without some flexing and that is the last thing you want when tapping something.
However, you may be able to do something with a stepper motor and suitably geared drive train. It all comes down to how often you are doing the plates and how much effort you want to put into a solution.
ShapeOko2 #3400 - Chinese 800W AC Spindle - Stiffened X-Axis - TR10 Z-Axis - Inverted Z Motor - Hall Effect Limits - Drag Chains & Custom Brackets

Hans
Posts: 290
Joined: Tue Dec 25, 2012 5:19 am
Location: Connecticut, USA

Re: Tapping aluminum plates

Post by Hans » Wed Feb 11, 2015 9:20 pm

You could build an X-Y table, mount it on your drill press, and use feed holds to wait for manual tapping after making each hole. How many of these are you doing? Have you considered a used, CNC tapping center? It's unlikely that designing your own machine is economical.

EDIT: A Bridgeport with DROs is a reasonable middle-ground.
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veng1
Posts: 250
Joined: Fri Nov 30, 2012 12:09 pm

Re: Tapping aluminum plates

Post by veng1 » Wed Feb 11, 2015 10:12 pm

I've been thinking about this hack for drilling holes in Al.

http://www.instructables.com/id/Hacking ... /?ALLSTEPS

Jimf
Posts: 233
Joined: Wed Feb 11, 2015 8:58 pm

Re: Tapping aluminum plates

Post by Jimf » Wed Feb 11, 2015 10:58 pm

What your describing is called rigid tapping on a mill. Kinda difficult to do unless you have a programmable spindle speed with reverse. Hoss did some experiments with stepper motor rigid tapping at http://hossmachine.info/projects_8.html. Take a look there for ideas.

I use a tapmatic on my cnc bench mill which works very well but it would be hard to make it work with a shapeoko.

Caesar S
Posts: 197
Joined: Mon Sep 29, 2014 7:19 pm
Location: Seattle, WA

Re: Tapping aluminum plates

Post by Caesar S » Thu Feb 12, 2015 12:04 am

I'm thinking a ShapeOko 2 used as an X/Y table, the wasteboard moves the plate around.

The z axis is used to control the Procunier plunge and retract.

So the drill press is the Z axis, the ShapeOko moves the plate around.

That might work, one 9 x 9 plate at a time, but hey, it's faster and better than doing it by hand.

Thanks everyone!

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