TC Tapper - Home Made

I bought a commercial tension compression tapper for use on my non-C-axis CNC mills. Took me only one buggered hole to get timing right so it would work. No compression, and very little extension testing on aluminum with good spiral point taps in sizes I commonly use. Then it took me only a couple tries to create a style in my style library that will produce good tapping code for it in my CAM software using a "scripted" drilling operation.
You would think that would be enough, but lately I've found myself tapping three different sizes commonly. My newest mill takes advantage of the tool table heights and does a good job, but if I am constantly swapping taps int he TC tapper I can't set the tool height in the table.
My solution. Make a couple more TC tappers. The first two blanks I destroyed on the lathe by trying to shade tree it. Nothing is really critical except that the bore for the tap holding collet chuck and the shaft of the TC tapper are concentric. Well on the third one I had some success, but I failed to get the proper alignment turning concentric. The tip of the tap orbits around the center of rotation. Its to much to just let slop in the TC tapper account for it. I actually tapped a couple test holes in aluminum with it, and it tapped them... over sized. LOL.
Mine is in front: http://bbs.homeshopmachinist.net/attachment.php?attachmentid@17&d 43523014
Anyway, I thought about my steps and processes and I know how to make the next one better. Now I am thinking about materials. The first ones were all made out of 304 stainless except the straight shank collet chuck which is some sort of modestly hard steel or so says my drill bits. I didn't pick 304 stainless because I thought it was good for the application. I picked it because it was the cheapest stock I had on hand that was the right size to start with. I've got some 4140QT TGP on hand. Its good stuff for making tools, but its a bit expensive to waste. My local metal yard (the one I like) has 1018, I think 1035, and 1144 Stressproof (tm) on hand along with oodles of 304 stainless. There really isn't going to be a lot of stress on the shank. The tap will likely break before anything slips. Still I'd like to use something I can put in the machine that isn't going to mess it up, but that I can machine without having to send out to heat treat. I'm leaning towards the 1144 stress proof. Its pretty strong, and it machines very nicely.

On 11/29/2018 1:24 PM, Bob La Londe wrote:> I bought a commercial tension compression tapper for use on my > non-C-axis CNC mills. Took me only one buggered hole to get timing > right so it would work. No compression, and very little extension > testing on aluminum with good spiral point taps in sizes I commonly use. > Then it took me only a couple tries to create a style in my style > library that will produce good tapping code for it in my CAM software > using a "scripted" drilling operation. > > You would think that would be enough, but lately I've found myself > tapping three different sizes commonly. My newest mill takes advantage > of the tool table heights and does a good job, but if I am constantly > swapping taps int he TC tapper I can't set the tool height in the table. > > My solution. Make a couple more TC tappers. The first two blanks I > destroyed on the lathe by trying to shade tree it. Nothing is really > critical except that the bore for the tap holding collet chuck and the > shaft of the TC tapper are concentric. Well on the third one I had some > success, but I failed to get the proper alignment turning concentric. > The tip of the tap orbits around the center of rotation. Its to much to > just let slop in the TC tapper account for it. I actually tapped a > couple test holes in aluminum with it, and it tapped them... over sized. > LOL. > > Mine is in front: > http://bbs.homeshopmachinist.net/attachment.php?attachmentid@17&d 43523014
> > > Anyway, I thought about my steps and processes and I know how to make > the next one better. Now I am thinking about materials. The first ones > were all made out of 304 stainless except the straight shank collet > chuck which is some sort of modestly hard steel or so says my drill > bits. I didn't pick 304 stainless because I thought it was good for the > application. I picked it because it was the cheapest stock I had on > hand that was the right size to start with. I've got some 4140QT TGP on > hand. Its good stuff for making tools, but its a bit expensive to > waste. My local metal yard (the one I like) has 1018, I think 1035, and > 1144 Stressproof (tm) on hand along with oodles of 304 stainless. There > really isn't going to be a lot of stress on the shank. The tap will > likely break before anything slips. Still I'd like to use something I > can put in the machine that isn't going to mess it up, but that I can > machine without having to send out to heat treat. I'm leaning towards > the 1144 stress proof. Its pretty strong, and it machines very nicely.
And I just checked. They have 1144 Stressproof on hand for just over half the price of McMaster.

On 11/29/2018 2:18 PM, Bob La Londe wrote:
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I was busy cutting molds and inserts all day today for customers, so I didn't have time to make another TC tapper. I did modify the first one I finished. All I did was bore out the nose and let the collet chuck slop around a little more. CNC tapped 20 holes to 10-32 holes with it. Looked a little sloppy, but as soon as it entered the hole it was nice and straight. The threads look good, and it didn't waller them out any. Maybe next week I'll have time to make a couple more. I bought some 1144, but that stainless one looks so pretty I'm tempted to make more of them out of stainless even though it is a little touchy to work with. Just changed one of my processes and order them a little better.

On Sat, 01 Dec 2018 19:56:13 -0700, Bob La Londe wrote:
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attachmentid@17&d43523014
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I hope you can post some more pictures, eg of the TC tapper parts before you assemble the others. My impression (or possibly misunderstanding) is that having a spring with the right spring constant is important to how well a TC tapper works -- how did you pick out what spring to use?

"James Waldby" wrote in message
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I hope you can post some more pictures, eg of the TC tapper parts before you assemble the others. My impression (or possibly misunderstanding) is that having a spring with the right spring constant is important to how well a TC tapper works -- how did you pick out what spring to use?
********** I have a pegboard on the back wall of my shop where I store salvaged parts. Springs, hose clamps, etc. I walked back to where I have springs, and I designed the tapper around a spring I just happen to have six of. I have one commercially made TC tapper, and I compressed the spring until it felt like it took the same amount of force to move it. Then I designed the TC tapper to have that much preload. I dropped the spring in the tapper body and pressed it in with my thumb to about the same preload, and marked it with a Sharpie marker. I snapped the spring at the mark. When I installed the springs I reversed the pieces so the flat ends ride against the cross pin. The pin wound up pretty close to where I wanted it.
I don't think spring selection is that critical. I mean I wouldn't use the spring out a self inking stamp pad or the coil spring out of a truck, but if you look at springs that are close to right size for the collet chuck and you have to start to load up the tendons in your hand to compress it you will be close. Worse comes to worse, if your spring is a little light you can tap the holes twice. Assuming it isn't so light that you use all the compression of your tool before it reverses. Once the tap is started in the thread, all the spring does is allow the tap to follow the thread if your synchronization isn't perfect. Unless you have a C axis spindle its never perfect, and it takes time to reverse the spindle at the bottom of the stroke. This is where selecting the right dwell time and a little planning is helpful. Steel might not be as forgiving as aluminum. This is one place I'd just have to run some tests and see.
I have two styles setup in my styles library for that machine in CAM now. Its pretty easy to do. My speed feed calculator (HSM Advisor) will do it, but it tends to want to suggest RPMs that are to low, or to high for my comfort level. Since I mostly run my machines in inch mode its pretty easy to calculate myself. Pick an RPM and divide by the TPI. Of course I had to semi script a "custom" the "drill" operation for dwell and reversal, but somebody else had already done it and posted about it on the CAM software forum. I only had a couple details to work out.
I set up my first test of the new homemade TC Tapper after the latest modifications running 20 holes with 10-32 threads in 6061-T6511 aluminum. I had only three holes where I could see movement as the tool exited the work piece. It looked to be about 1 thread. I'd say the TC tapper did the job. I'm not brave enough to tap blind holes with it just yet, but it does a passable job on through holes using a spiral point tap.
I'm considering making a video of the process, but making a video, setting up cameras and planning shots makes any job take twice as long.

"Bob La Londe" wrote in message
  Quoted Text Here  
I hope you can post some more pictures, eg of the TC tapper parts before you assemble the others. My impression (or possibly misunderstanding) is that having a spring with the right spring constant is important to how well a TC tapper works -- how did you pick out what spring to use?
********** I have a pegboard on the back wall of my shop where I store salvaged parts. Springs, hose clamps, etc. I walked back to where I have springs, and I designed the tapper around a spring I just happen to have six of. I have one commercially made TC tapper, and I compressed the spring until it felt like it took the same amount of force to move it. Then I designed the TC tapper to have that much preload. I dropped the spring in the tapper body and pressed it in with my thumb to about the same preload, and marked it with a Sharpie marker. I snapped the spring at the mark. When I installed the springs I reversed the pieces so the flat ends ride against the cross pin. The pin wound up pretty close to where I wanted it.
I don't think spring selection is that critical. I mean I wouldn't use the spring out a self inking stamp pad or the coil spring out of a truck, but if you look at springs that are close to right size for the collet chuck and you have to start to load up the tendons in your hand to compress it you will be close. Worse comes to worse, if your spring is a little light you can tap the holes twice. Assuming it isn't so light that you use all the compression of your tool before it reverses. Once the tap is started in the thread, all the spring does is allow the tap to follow the thread if your synchronization isn't perfect. Unless you have a C axis spindle its never perfect, and it takes time to reverse the spindle at the bottom of the stroke. This is where selecting the right dwell time and a little planning is helpful. Steel might not be as forgiving as aluminum. This is one place I'd just have to run some tests and see.
I have two styles setup in my styles library for that machine in CAM now. Its pretty easy to do. My speed feed calculator (HSM Advisor) will do it, but it tends to want to suggest RPMs that are to low, or to high for my comfort level. Since I mostly run my machines in inch mode its pretty easy to calculate myself. Pick an RPM and divide by the TPI. Of course I had to semi script a "custom" the "drill" operation for dwell and reversal, but somebody else had already done it and posted about it on the CAM software forum. I only had a couple details to work out.
I set up my first test of the new homemade TC Tapper after the latest modifications running 20 holes with 10-32 threads in 6061-T6511 aluminum. I had only three holes where I could see movement as the tool exited the work piece. It looked to be about 1 thread. I'd say the TC tapper did the job. I'm not brave enough to tap blind holes with it just yet, but it does a passable job on through holes using a spiral point tap.
I'm considering making a video of the process, but making a video, setting up cameras and planning shots makes any job take twice as long.
***********
If you make one, plan on breaking some taps and run tests on pieces of metal off your scrap pile. I ran one test, modified the tool, and then used it on a real work piece. Well, sort real. It was the backing plate for a full profile glue and tape mounted job where I drilled holes, flycut to proper thickness, and then screwed down through all the holes before cutting 360 degree profile parts full thickness. I guess it was a real fixture plate as opposed to a real part, but the results were passable. So far I have not broken a tap. I had used the commercially made tapper on one similar job before deciding I wanted atleast three of these tools in my tool rack for this machine.