Tap and die woes

[Dan_F]

Well, I've been experimenting with the tap and die and not having much luck. I think that the die operation is the problem. When I look at the die threads with a loupe , they are most crisp at the forward end (last cut), and progressively less so toward the beginning end (tailstock), where they have been run over each time I back out. I can't really see the cap threads very well, as they are set in about 1/2" from the lip.

I'm going with a 7/16" hole for the tap, and .475" tenon for the die as was suggested in another thread. I cut 5/16" of thread on the tenon, and a tad more in the cap. I can just barely get one full turn of the two parts, but it takes a lot more oomph to get there than with my Churchill. I tried using the Churchill cap on my threads for comparison and it too required more force than the actual pen does.

So, I'm wondering what I'm doing wrong.

How often do you back out to clear the chips, and do you back out all the way or just a bit? I have been backing out all the way and clearing the curlies from the die about every 1/4 to 1/2 revolution. I hold the barrel in a collet chuck, and have a die holder with a morse taper that fits in the tailstock. I let the die draw the tailstock forward as was suggested in the tap and die thread. The tailstock for my PowerMatic is quite heavy, at least 50 pounds. I don't know if that's too much weight for the die to pull or not.

I'm using PAM cooking spray for lubrication.

Is it possible the die is not adjusted properly? It has a set screw which appears to open it up or close it down. How do I check it? I have a dial caliper that reads thousandths.

Any other tips or advice is welcome. I have very little experience with such things. Tapping the threads for the section seems to go all right, except that I have to hold the tap manually because that tap won't pull the tailstock forward, the threads just strip right out. The section threads in nicely though.

I've done two barrels and three caps, and there is no consistency of fit between them. I'm hoping that improving technique or adjustment of the die will help.

Dan

 

[randyrls]

Well, I've been experimenting with the tap and die and not having much luck. I think that the die operation is the problem. When I look at the die threads with a loupe , they are most crisp at the forward end (last cut), and progressively less so toward the beginning end (tailstock), where they have been run over each time I back out. I can't really see the cap threads very well, as they are set in about 1/2" from the lip.

I'm going with a 7/16" hole for the tap, and .475" tenon for the die as was suggested in another thread. I cut 5/16" of thread on the tenon, and a tad more in the cap. I can just barely get one full turn of the two parts, but it takes a lot more oomph to get there than with my Churchill. I tried using the Churchill cap on my threads for comparison and it too required more force than the actual pen does.

So, I'm wondering what I'm doing wrong.

How often do you back out to clear the chips, and do you back out all the way or just a bit? I have been backing out all the way and clearing the curlies from the die about every 1/4 to 1/2 revolution. I hold the barrel in a collet chuck, and have a die holder with a morse taper that fits in the tailstock. I let the die draw the tailstock forward as was suggested in the tap and die thread. The tailstock for my PowerMatic is quite heavy, at least 50 pounds. I don't know if that's too much weight for the die to pull or not.

I'm using PAM cooking spray for lubrication.

Is it possible the die is not adjusted properly? It has a set screw which appears to open it up or close it down. How do I check it? I have a dial caliper that reads thousandths.

Any other tips or advice is welcome. I have very little experience with such things. Tapping the threads for the section seems to go all right, except that I have to hold the tap manually because that tap won't pull the tailstock forward, the threads just strip right out. The section threads in nicely though.


Dan

Dan; I have not done tapping on pens, just metal. You probably already know this!

Never do tapping under power!

The tap or die should always be free to move forward. They should not be firmly attached to the tail stock.

There are tap handles with a round bar sticking out the opposite end from the tap. Insert the bar into a jacobs chuck or collet in the tail stock. You should be able to slide the tap back and forth. Turn the tap manually using the "T" handle

The tap or die should be reversed every 1/4 to 1/2 revolution. Back it off about the same amount.

Thread the tap into the die and make sure they match. Use the adjustment screw to ensure a good match.

The die should not be attached firmly to the tail stock.

 

[Texatdurango]

... I'm going with a 7/16" hole for the tap, and .475" tenon for the die as was suggested in another thread. ...Dan

I try to get my tenons close to .468". I have made dozens of pens with the tap/die set with good results in acrylics, polyesters and truestone.

You might want to try a slightly smaller tenon once to see what you think.

 

[LEAP]

Dan,
In softer materials I have been screwing a threaded dowel on the inside of the barrel for support while I'm using the die for the outside threads. It seemed that the unsupported tenon was collapsing just a hair when using the die. I did have to adjust the die just a bit to get it to match the tap. Once that was set the rest of the process went smoothly.

 

[rherrell]

Dan, get yourself one of these http://tinyurl.com/5lqwxq
It slides about 2" so no more dragging that heavy a@# tailstock around.I have one and wouldn't think of threading without it.

 

[Dan_F]

Thanks, your replies have been helpful.

I have the die holder that Rick linked to, though didn't know that I could let it slide like that, I had it locked and turned the lathe by hand. The darned thing didn't come with directions.

Can I back up a 1/4 turn as with metal, or should I back out all the way each time to clear the swarf?

The die, as it turns out, required quite a bit outward adjustment to allow the tap to enter it, that should make a big difference.

I'll look for a tap holder like Randy mentioned.

Thanks again.

Dan

 

[ed4copies]

Do you use a lubricant?

I've not done pens yet, but when tapping metal, cutting oil sure helps!!

 

[Dan_F]

Do you use a lubricant?

I've not done pens yet, but when tapping metal, cutting oil sure helps!!

Yes, Pam cooking spray is what people seem to be getting the best results with.

Dan

 

[Glass Scratcher]

Dan, get yourself one of these http://tinyurl.com/5lqwxq
It slides about 2" so no more dragging that heavy a@# tailstock around.I have one and wouldn't think of threading without it.

Apparantly one of my security settings isn't letting me access the tinyurl site. Could you post the regular URL?

 

[DCBluesman]

http://littlemachineshop.com/products/product_view.php?ProductID=2314&category=

 

[Dan_F]

Glass Scratcher and Lou---That's the one I have that I now know how to use.

Dan

 

[Glass Scratcher]

Pity it only comes in a MT2. One of these days I will have a grown-up lathe.

 

[rherrell]

I thought some photos might clear up a few things.
First is a photo of the die holder in use....

It slides on a straight shaft and I turn it by hand.
Here's a photo of the set up I use for internal threads....

The part you see in the Jacobs chuck I made myself. It's the key to the whole process. Here's a drawing......

I made mine from steel but I don't see why a good hardwood couldn't be used. It's spring loaded so it automatically keeps feeding the tap. It also keeps everything perfectly aligned.
On the right is the die holder. It's made for the round dies. 1" on one end and 13/16" on the other. Hex dies won't work.

 

[handplane]

I've been searching and cannot seem to find the tap and die information. Is there a special type for the four start threads? Is there also a special type for cutting plastic? I cut metal threads at work regularly but have not tried it on plastic or wood yet.

 

[Dan_F]

I've been searching and cannot seem to find the tap and die information. Is there a special type for the four start threads? Is there also a special type for cutting plastic? I cut metal threads at work regularly but have not tried it on plastic or wood yet.

There was a group buy a while ago for custom 3 start tap and die of the same size as the El Grande/Churchill kits. Apparently it wasn't specified to be used for plastic, so something about it is not optimal. They pop up for sale every now and then in the forum marketplace. Price for the pair was around $200, but for a single pair would have been around $500.

Dan

 

[BRobbins629]

I have seen several comments regarding the fact that the triple start taps and dies are not optimal for plastic. The most knowledgeable say that they do not have the optimal rake angle for plastic. Although I have not tried to use 2 taps with different rake angles, I do know that many nice pens that are quite functional have been made using these sets with threads cut in aluminum, PR, Ebonite, Truestone, and Aluminite. There have also been a number of cracked barrels and failed attempts, but that's usually the price we pay for trying something new and I don't believe is related to the tap or die design. The factory that made them was sent a coupler from an El Grande set and asked to provide a specification and sets to match those threads. For me, this has opened up many design opportunities and now my FP kits consist of a $4.00 nib. Dan is correct about the pricing.

 

[gwilki]

My threads were tight until I got good advice from George (Texatdurango). He showed me how to lightly scrape the threads with an Xacto knife held almost 90 degrees to the thread. A couple of very light scrapes and my threads are smooth as silk.

 

[scubaman]

I completely agree, Bruce. I had raised that question of rake angle, not to put this set down, only to find out what had been ordered. It may not be ideal but it is certainly functional! There are differences between materials, and all plastics do not thread the same. Find which work and use those And your threads get better with practice unless you do something fundamentally wrong

Re. tooling: For dies, I use a die holder like the one from littlemachineshop.com that has been mentioned and what Rick showed in his photos. It works very well. Here's a hint that may help new threaders: Most dies are tapered on one side (the stamped front) to make them easier to start. The backside is often not tapered. This can be used to get a little closer to a shoulder: Cut using the front, then reverse the die and chase the thread up to the shoulder. You don't gain much but sometimes that little bit makes a difference!

There was a question above about adjustable dies that I believe was not answered. On adjustable dies, if you tighten the setscrew, you expand the die a little. You use the screws on your die holder to collapse the die - the collapsed diameter is determined by how far the setscrew is backed out. The nominal position is 'neutral' where the setscrew goes in till it contacts the taper.

I tap using a device just like what Rick showed - only I was lazy and bought mine from littlemachineshop. Instructions for making one are shown on mini-lathe.com, as a suggested introductory project for your new minilathe. I just lookedf and can't find it... maybe the site owner moved it over to the premium content which you have to pay for?

 

[Dan_F]

Ok, here is a progress report.

I tried to adjust the die as someone had suggested, by threading the tap into the die. In order to do this, I had to open up the die a significant amount. Once in to the end of the die, I got it as snug as possible by closing it down gently until the tap would no longer turn, then opening it back up just enough to turn the tap back out. I then tried to insert the die into the holder, but it would no longer fit, so I had to close it back down enough to go back into the holder.

I tried this setting on a tenon of .466, and got relatively shallow threads, so tightened it a little more and got some decent but not great threads, the bottom of the grooves were fairly flat, and the peaks were not too sharp either, but better than before. There was some variation in the height of the peaks as well, which I thought odd. I did about three different tenons, the fit is very inconsistent, with most being too tight after about a half turn, but loosen up a bit when worked repeatedly.

Today I tried to find a tap wrench with the sliding feature that would function similar to the die holder, but couldn't find one locally. I ordered one, but shouldn't get it until Monday. I ended up making my own out of a standard T tap wrench, which had a small hole in the back, into which I inserted a transfer punch, which in turn slides into a drilled 1/2" dowel which is seated in a Jacob's chuck. It actually works pretty well. I think the reason that my fist attempt a couple of days ago sort of worked is because dragging that heavy tail stock must have taken off just a hair more material.

The threads from the tap look pretty good, better than those from the die. I did two taps tonight, and now none of the tenons I did last night will go in either tapped hole. Neither will the tenon from my Churchill. Well, it just barely starts, then gets stuck. It doesn't appear to be cross threading. I tried the second tap using another drill bit, thinking that the first one might have been a little undersize, but they both came out the same. I also waited a while to let the black cool before tapping it, but it still came out the same. The wall is about 1/8", the stock being 3/4" rod from Woodturningz IIRC.

When you operate the tap, do you have the stock all the way into the collet so that is prevents the stock from expanding during the operation? I tried that while running the tap a second time into the same hole, but it didn't make any difference.

I measured the tenons, and they read .465, .466, and .468 after using the die.

The next step will be to tighten down the die even more, this time relaxing the adjusting screw to have some slack in it and closing it down with the two exterior set screws. In the mean time, if anyone can see something I'm missing, please feel free to comment.

My question about whether it is necessary with plastic to back all the way out with either tap or die to clear the swarf rather than just back up a quarter turn then continue forward until finished is still on the table. I know you just need to back up a bit with metal, but is it the same with plastic?

Edit: Didn't see Grant's post about scraping the threads, will try that too. Does anyone else find that they need to do that?

Dan

 

[Dan_F]

Here are some pics of the tenons I've threaded. The T formation was done last night, the others a couple days ago. The one on the far right that looks really flat was actually taken down a hair with a scraper after it was threaded, as it was too tight and I wanted to see if it would help. How do these compare to what you are used to seeing? They certainly aren't as sharp as those on my Churchill.


Edit: OK, just finished one more tenon, turned to .466, after threading was .454. It fit into the taped holes better, actually a little sloppy now. The threads still look pretty funky through a 10X loupe, one is thread doesn't look too bad, the other two are more abraded and lower than the other one. This was done without backing all the way out to clear the swarf, just going back a quarter turn. Pam cooking spray was used as a lubricant.

Question: If everything is set properly, should one expect the finished OD to be different from what is measured before threading? If so, how much? My last example differed by about .012". What, if anything, should that tell me?

Dan

 

[rherrell]

Just a thought, if you're not already, try going for 75% thread engagement when you thread internally. Here's a calculator....http://tinyurl.com/5u5vcr...Put in your outside diameter and your TPI (pitch for metric) and it'll spit out the hole size you need.
Also, try reducing your tenon diameter AT LEAST 1% from nominal. As an example for a 1/2" thread --- .500" X .01 = .005"
Make your tenon .495" instead of .500". Personally, I take off more than that but start with 1% and see if that helps.

 

[Dan_F]

Rick---Thanks, I'll check that out tomorrow.

After one more go at it, here's what I've learned tonight: Threads definitely look nicer when I back all the way out every quarter turn and clear out the swarf thoroughly.

I lose about .015" OD after running the die with adjustment band "at rest". At this setting, on a .474 tenon, the difference between the peak and valley of thread is .013"

It was a little too tight, so I tightened the die a little bit and ran it again. After that, the OD was .456. a difference of .0065 from the previous setting. The difference between peak and valley was .011, and the threads looked rattier. The difference between the valley of the first setting and the valley of the second is .0045. After the second treatment, the fit was looser, a little sloppy even.

Tomorrow I'll try a smaller tenon at the relaxed position and see what happens. Will also try to make sense out of what Rick suggested. Tech talk makes me dizzy.

Dan

 

[Ligget]

I have just taken delivery of my tap and die sets, have got the die holder coming over the pond from The Little Machine Shop, this is a great `thread` to follow as I am a complete beginner with taps and dies. :glasses-nerdy: