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  #11 (permalink)  
Old 01-21-2011, 06:32 PM
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Default Re: Trouble with a Mini-Lathe Controller

Ron, I guess you mean spiral flute taps?



Don't think I have any spiral flute taps but spiral point taps
seem to work fine by hand. That said, I seldom use a tap handle.
I've been using cordless drills for tapping for 20 years. If it needs
to be dead square I start in the drill press by hand and if the material
is too thick to finish there I move to a bench and use the cordless drill.

With the electric brake and high torque you can stop immediately
when you feel the strain is too high. I don't remember even breaking
a tap but I sometimes have a problem with slippage in the chuck.

By the way it looks like the wikipedia page on taps needs to be beefed up if you have some time.
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  #12 (permalink)  
Old 01-21-2011, 08:14 PM
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Default Re: Trouble with a Mini-Lathe Controller

Yes, Ron meant spiral flute, the other spiral is a common tap and should be the most common.

Since this has turned into a discussion on taps, does anyone have any experience with Thread Forming taps, aka Roll taps? It sounds like these might be ideal for the blind holes in my Rail Dogs.
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  #13 (permalink)  
Old 01-21-2011, 08:36 PM
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Default Re: Trouble with a Mini-Lathe Controller

Yes, those are the ones. The chips made are continuous much the same as with a twist drill bit. When used in machining centers holes can be tapped at high speeds of around a couple thousand RPM's with the spindle immediately reversing -- no breakage. By hand, not so much.
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  #14 (permalink)  
Old 01-21-2011, 10:15 PM
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Default Re: Trouble with a Mini-Lathe Controller

Steve, I've used an M8 thread forming tap in aluminum extrusions and flat stock. It is a good choice for thin walled stuff because the material displaced actually increases the thickness of the hole. The tapered version was easier to start in the ribbed center hole of my Bosch T-slot extrusions. I see that 8020 doesn't have the ribs, just a nice round hole so regular cutting taps should center well.

That said, these taps swage rather than cut and they require a lot more torque than cutting taps although the load is constant and you don't need to reverse the tap to clear out swarf. Securing a round rod and running a thread forming tap into the end might be difficult to do without scoring or embossing the sides of the rod. I wonder if you could swage/tap the hole before you turn the dog down to final size....could you hold the dog securely enough via a screw in the chuck of the lathe?

Doh!!

I just realized the dog itself (or rather a hunk of the same rod that will be cut off) will be in the lathe chuck and you just put the tap in the chuck on the tail vise. Plenty of torque and concentricity. Might work great.

"Unlike thread cutting, no material is removed during thread forming. Rather, the process displaces the material to generate the thread form. Since the metal's structure is cold worked along the thread profile, the threads produced are generally stronger and have a smooth, burnished surface finish."
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  #15 (permalink)  
Old 01-21-2011, 10:27 PM
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Default Re: Trouble with a Mini-Lathe Controller

Being a blind hole, this is something I would do by hand or at very slow speed in the lathe. This mini-lathe doesn't have much torque so I have some concerns using it.

I've heard the tap has no cutting edge but I've also heard when the taps dulls it requires twice as much torque.
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Old 01-21-2011, 10:47 PM
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Default Re: Trouble with a Mini-Lathe Controller

I didn't use the thread forming tap enough to dull it.
I can't remember if I used lubrication but it is recommended.

Even at very slow speed it wouldn't take long in the lathe.
And, with no clean-up except to wipe off a little lubricant
it might be just as fast or faster compared to cutting thread.
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  #17 (permalink)  
Old 01-21-2011, 10:57 PM
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Default Re: Trouble with a Mini-Lathe Controller

After using "Tap Magic" cutting fluid with my taps, I would never tap again without fluid, or a wax compound that I use with aluminum. I see with the Roll taps they recommend a lubricant more than a cutting fluid. I haven't seen a website that recommends a fluid but I'm sure my handy gallon of WD-40 would do the trick.

Perhaps Aluminum is soft enough that I won't have to worry about dulling the tap.
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  #18 (permalink)  
Old 01-21-2011, 11:51 PM
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Default Re: Trouble with a Mini-Lathe Controller

Quote:
Originally Posted by MichaelKellough View Post
Steve, I've used an M8 thread forming tap in aluminum extrusions and flat stock. It is a good choice for thin walled stuff because the material displaced actually increases the thickness of the hole. The tapered version was easier to start in the ribbed center hole of my Bosch T-slot extrusions. I see that 8020 doesn't have the ribs, just a nice round hole so regular cutting taps should center well.

That said, these taps swage rather than cut and they require a lot more torque than cutting taps although the load is constant and you don't need to reverse the tap to clear out swarf. Securing a round rod and running a thread forming tap into the end might be difficult to do without scoring or embossing the sides of the rod. I wonder if you could swage/tap the hole before you turn the dog down to final size....could you hold the dog securely enough via a screw in the chuck of the lathe?

Doh!!

I just realized the dog itself (or rather a hunk of the same rod that will be cut off) will be in the lathe chuck and you just put the tap in the chuck on the tail vise. Plenty of torque and concentricity. Might work great.

"Unlike thread cutting, no material is removed during thread forming. Rather, the process displaces the material to generate the thread form. Since the metal's structure is cold worked along the thread profile, the threads produced are generally stronger and have a smooth, burnished surface finish."
The roll taps make a much stronger treaded hole as Michael said. No material is taken away.
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  #19 (permalink)  
Old 02-23-2011, 11:24 PM
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Default Re: Trouble with a Mini-Lathe Controller

Here is a follow up for those monitoring this thread.

I was going to get a spiral flute tap to play with but everyone of them were fast spirals with a 53 degree helix. I know it would have worked okay but if I'm going to get one, I will watch for a slower speed spiral.

I did order a Vega 1/4-20 roll forming tap, H3 fit. It arrived this week and I found some time to play with it today. It requires you to drill #1 (.228") hole instead of the normal #7 (.201") hole. I have a #1 drill bit but it wasn't real sharp, I should have spent a few minutes and sharpened it.

Drilled 3 practice holes in some aluminum scrap Rail Dogs to play with. The first I wanted to hand tap with the roll tap. I put some Tap Ease wax on the tap and that baby went in with no problem. The required pressure was just a little bit more that a normal tap but not enough to be of any concern with my Mini-Lathe.

The second hole I power fed with the lathe. The lathe stalled close to the end so I reversed it out and check it. It didn't get to the end of the blind hole so I hand started the tap and power fed some more. Once I was done this thread was flat on the tops, doesn't look the greatest but it works just fine.

For the last hole I monitored the tap depth a little better. When the lathe stalled, I backed up the tap a little (without removing it), and then drove it a bit deeper. On this one the thread has a double crown on the top almost looking like a double thread. Once again, it doesn't look the greatest but it works just fine.

Power tapping shouldn't make any difference in the appearance of my threads. I suspect that was due to the dull drill bit. Since I will start using this regularly, I'm going to buy a good #1 drill bit. I will sharpen the one I have and keep it as a spare.

The fit with the screw threads were much better than with my other taps but I'm not sure if those taps are H3 or maybe H5. It is really nice not having any debris to clean out of the freshly tapped holes.

I didn't do any tests for strength since my immediate use doesn't require strong threads. There is no reason to believe the threads wouldn't be strong but I will test for that at some later date.

I will be picking up some roll forming taps for my other common sizes.
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  #20 (permalink)  
Old 02-24-2011, 12:26 AM
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Default Re: Trouble with a Mini-Lathe Controller

The design engineers that I used to work with did quite a lot of analysis when we first tried roll taps -- they were happy with the higher strength in shallow holes, etc. The roll taps do require more horsepower.
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