Tapping machine idea

churchjw

churchjw

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I am starting to build (thinking about starting) a pneumatic tapping machine. I saw one of these at a tool show about a year ago. Not sure it was this brand but it was similar. http://www.lans.com.tw/10-tapping_machine.html I have a heavy duty computer monitor arm that is as stable as the tapping machine arm I played with at the show. Not as much range of motion. I am thinking of using a reversible impact air screwdriver with a pressure regulator as the driver. http://www.harborfreight.com/reversible-air-screwdriver-90059.html It even looks like what they were using in the professional version. The guy wouldn't say but it felt like an impact wrench when it tapped holes. I would need to add a tap holder to the end but that looks easy enough.

So my question to the group does this look doable or am I missing some big problem? Has anyone on here built something like this and if so what were the problems?

As I see it I have to have a way to hold the tap, control torque, and keep it square to the work piece. Anything I am missing. This would just be for smallish taps ie 6-32 to 1/4-20.

Jeff
 
churchjw said:
I am starting to build (thinking about starting) a pneumatic tapping machine. I saw one of these at a tool show about a year ago. Not sure it was this brand but it was similar. http://www.lans.com.tw/10-tapping_machine.html I have a heavy duty computer monitor arm that is as stable as the tapping machine arm I played with at the show. Not as much range of motion. I am thinking of using a reversible impact air screwdriver with a pressure regulator as the driver. http://www.harborfreight.com/reversible-air-screwdriver-90059.html It even looks like what they were using in the professional version. The guy wouldn't say but it felt like an impact wrench when it tapped holes. I would need to add a tap holder to the end but that looks easy enough.

So my question to the group does this look doable or am I missing some big problem? Has anyone on here built something like this and if so what were the problems?

As I see it I have to have a way to hold the tap, control torque, and keep it square to the work piece. Anything I am missing. This would just be for smallish taps ie 6-32 to 1/4-20.

Jeff
Click to expand...

Never seen one before but doesn't mean it isn't doable. Will need a good regulator with a moisture trap and oiler, I didn't see one HF's website. Make sure you use two fluted taps, they are stronger than four fluted ones. Nice project.
 
Intriguing concept...

A question, though. Why does it need to be pneumatic? I have been tinkering with building me some sort of automated tapping machine, but I was thinking about using one of those battery operated drills. It should be easy to reverse direction. I am of course thinking of the electric implications, not the mechanical ones.
 
Using the drill is a good idea. You already have the torque control challenge partly covered.

"Billy G"
 
I thought about the drill idea. I have used my hand drill to run some larger taps through thin stock before. I was thinking that the shorter impact turning of the wench would be better for the tap. Now I am wondering if the impact from the wrench is linear to the shaft (ie hitting outward like a hammer drill) or rotational. If it is linear to the shaft then it won't work. The one I tried had a knocking feel for lack of a better word like a impact wrench. It turned the tap with short turns. Do you think I would get better torque control with the electric screwdriver vs the pneumatic? I would be afraid that the electric would have to low a torque and low speed but I guess gearing would fix that.


Jeff
 
Although I am not a mechanical expert, it seems to me most battery based drills will surpass the torque of a pneumatic tool. These drills already have a planetary gear head, which in my opinion is one of the strongest power transmissions you can get on a confined space (again, not a mechanical expert, so this statement can easily be flawed). If at all, you may need to switch it to the SLOW speed setting to get the torque you need to tap heavy stock, but this is not a high speed application anyway.

Do note that if you want a speed controller for any of these drills, it will need to take on humongous currents (100A are not unheard of on these drills). I am a motor driver designer with a few year's worth of experience. If this is something the community can greatly benefit from, I can easily design a microcontroller based speed controller which should be able to drive the 100A. Won't be tremendously cheap, but shouldn't be too expensive either. I am thinking no more than $30-40 dollars in components. FETs are pricey, when you want to run 100A loads...
 
Three of most important things with a tapping head is adjustable torque limiting, alignment, and lubrication. I have several automatic tapping heads and they can spoil you quick. I always have at least one setup in one of my drill presses. The automatic tapping heads also have a reversing clutch and gearing that allows the tap to instantaneously reverse when downward pressure is removed. Some units also increase the reverse speed for faster tapping. They're fast and almost never break a tap if set up properly.

A drill with a torque limiting chuck held in a cheap drill press stand or parallel arm would the closest low cost option. A drill could be rewired to make reversing automatic too. I just don't know how good it would be with small taps. Some pneumatic screw drivers have a built in torque limiter, but I'm not sure about the HF model you listed. Better units are as expensive as a real tapping head...
 
Jeff

How many holes are you planning on tapping in a day? Is this going to be for production or just your hobby shop?

I've power taped 4-40 into steel (backing plate in a control box) with an extension and didn't break a single tap with a cordless drill. I used it on and off for a week or so. There were after build changes on a few machines and I either had to remove the backing plate in the box or get a drill and tap in there some way.
 
I don't tap that much so this is just for hobby. It was more about making a new tool :) I know no one here would do something like that. Sounds like getting an electric drill is a better option or just buying a tapping head. LOL

Jeff
 
I have used a cordless drill for tapping numerous times. Mostly in the field and for jobs that were non-critical. I always use a clutch.

I remember doing about 40 holes of 3/8 16 thread in 3/4" aluminum stock. I broke one 1 tap when I got lazy from the monotony. Basically I was too aggressive and gave it too much throttle, the tap grabbed, and the drill torqued off axis when I caught the drill, snapping the tap.

IMO totally avoidable.

I think you could hack the drills (electrical) reverse switch and add an button to do your reversing.
 
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