A bottom tap question

[Larry (Omaha)]

I am not even close to being a machinist, but do have limited skills with metal. I have tapped many a hole installing door hardware over the years using a taper tap. My underhammer project requires me to drill and tap into a 3/4" breech plug for a musket nipple. (I am not working on a musket) The nipple is 1/4-28 and will extend to a coned cavity. I can't drill deep enough to use a taper tap, so a bottom tap is necessary. Here is the question: Will I be able to start the treads with a bottom tap? I plan on using my drill press to keep the tap perpendicular to the hole. I thought about a plug tap first, but not sure I have enough depth.
Thanks in advance

 

[painter]

IMO, you'd be better off starting the threads with a taper tap. You can grind some of the taper off if depth is limited.

 

[bang]

Use the tapered tap first. May have to sacrifice one by trimming the length to get a good thread. Once you have good enough threads that the bottoming tap will get a decent start cut final threading gently. Try the nipple and continue till it will thread in.

 

[Davey Boy]

Stop. Are you going to use the drill press Chuck to hold the tap?

 

[JHB]

Good advice above.Trying to start with a bottom tap will more times than not take out the first tooth and then you have a tap that ts scrap unless you can sharpen back past the chipped tooth.

 

[ohio ramrod]

The machinist handbook calls for three steps, taper tap, then , plug tap, finish with bottom tap. That has been repeated for over fifty years. I worked in a production shop as a tool grinder and tool and die man for over thirty years. We tapped many thousand holes directly with bottom taps in production runs. For tooling work we used a plug tap and then finished with bottom taps . Simply because we were working with tool steel while production used cast iron or aluminum. I recomend plug and finish with bottom tap.

 

[user 34300]

It is very important not to freehand this job.

Set the barrel in the drill press or milling machine vice. Drill the tap hole in steps. IF you drill all at once with a #3 you will get an oversized hole. Do not break the set up. Use the chuck to hold the tap directly or use a spud in the chuck to align the tap perfectly. Disable the the quill return spring on the drill press to guide the tap. Tap the hole with your taper of plug tap. Grind a bit off and go further. Grind the rest off making a bottoming tap. Finish the hole.

 

[Larry (Omaha)]

Stop. Are you going to use the drill press Chuck to hold the tap?

I do, plan on the drill press chuck holding the tap. How else can the tap be held in a ridged aligned position?

 

[Davey Boy]

What Scota@4570 said is excellent advice.

I would add this:

Use a spring loaded following center, the ones I use are made by Micro Tap.

Use tapping fluid, I like Tap Magic.

I don't understand the coned cavity, but when drilling the hole, the drill bit cannot have a sideways cut or it can easily shatter. Same with the tap.

I can go into further detail but I need to use a keyboard and not finger tap on this little screen.

Dave

 

[Davey Boy]

Bill Raby has videos on YouTube that show building a rifle that are absolutely terrific. His videos are really worthy to watch and he takes his time doing what I think is really good work.

I want to address drilling speed, you are doing one hole, you don't need production speeds and flood coolant. Make the barrel secured so it will not move as has already been said, but it is really important to get a good job done. Set the speed to a low setting like 130RPM, not screaming fast. Let the drill bit make nice easy cuts and don't force it to the point you are generating smoke and heat. You can use a cutting fluid, WD 40, kerosene, liquid soap or similar. You can also blow a stream of air on it. It cools the cut and flushes away the chips. You can drill it without fluid, cooling , whatever but keep the chips clear.

If you drill a little, pull back, drill a little, it will make a nice hole and you are less likely to screw up.

Have control of the drill feed so it doesn't grab the work and suck itself into it. So a drill press is great for that. If the work isn't held down and the drill grabs the cut, it can hurt you, break the drill bit, or make you regroup.

Here is a picture of a tap, tap handle, and spring loaded tap guide


The tap guide shown at the bottom is 1/2" diameter into a chuck which in your instance is the drill press chuck. The pointed end is spring loaded and the point fits into the centering hole in the tap handle. When you clamp your rifle barrel to the drill press table, the tap follower is in the chuck and is in alignment with where you want the hole in the barrel. The tap follower point is spring loaded and can be pushed in against the spring (one shown will move 1/2"). Set the distance from the chuck to the table so the tap follower, Tap handle with tap, and the barrel are in alignment and the tap follower is compressed enough to hold everything together. You want the tap follower to always have the spring pressure on the tap so it stays lined up as to turn the tap handle. Same thing when you are backing the tap out, don't allow the tap follower to bottom out compressed as you remove the tap.

It won't hurt a thing to practice doing the setup on a piece of scrap metal so you will know what to do on the barrel.

When tapping metal I really like the stuff shown in the bottle.

 

[Larry (Omaha)]

Bill Raby has videos on YouTube that show building a rifle that are absolutely terrific. His videos are really worthy to watch and he takes his time doing what I think is really good work.

I want to address drilling speed, you are doing one hole, you don't need production speeds and flood coolant. Make the barrel secured so it will not move as has already been said, but it is really important to get a good job done. Set the speed to a low setting like 130RPM, not screaming fast. Let the drill bit make nice easy cuts and don't force it to the point you are generating smoke and heat. You can use a cutting fluid, WD 40, kerosene, liquid soap or similar. You can also blow a stream of air on it. It cools the cut and flushes away the chips. You can drill it without fluid, cooling , whatever but keep the chips clear.

If you drill a little, pull back, drill a little, it will make a nice hole and you are less likely to screw up.

Have control of the drill feed so it doesn't grab the work and suck itself into it. So a drill press is great for that. If the work isn't held down and the drill grabs the cut, it can hurt you, break the drill bit, or make you regroup.

Here is a picture of a tap, tap handle, and spring loaded tap guide

The tap guide shown at the bottom is 1/2" diameter into a chuck which in your instance is the drill press chuck. The pointed end is spring loaded and the point fits into the centering hole in the tap handle. When you clamp your rifle barrel to the drill press table, the tap follower is in the chuck and is in alignment with where you want the hole in the barrel. The tap follower point is spring loaded and can be pushed in against the spring (one shown will move 1/2"). Set the distance from the chuck to the table so the tap follower, Tap handle with tap, and the barrel are in alignment and the tap follower is compressed enough to hold everything together. You want the tap follower to always have the spring pressure on the tap so it stays lined up as to turn the tap handle. Same thing when you are backing the tap out, don't allow the tap follower to bottom out compressed as you remove the tap.

It won't hurt a thing to practice doing the setup on a piece of scrap metal so you will know what to do on the barrel.

When tapping metal I really like the stuff shown in the bottle.

Davey Boy,
I really appreciate the good information. I was going to rotate the chuck by inserting a punch in the key hole with the tap in the chuck. I like the following center suggestion better.
One of your other replies questioned "coned" by me. This is the critter I am currently working on.
I only get one chance to drill and tap it correct.
Larry

 

[Davey Boy]

In the illustration shown below, the arrow indicates the danger point for a drill or tap. If the cutting edges of drill or tap hit and catch, the drill and/or tap can easily break. You are correct in the location needing to be as shown in your illustration, any deviation would not be correct.

I assume the counterbored hole in the barrel through to the breech plug is already done for you. If so, centering in that hole gives you a perfect location for the drill/tap operations.

Just do a solid set up and go easy and it will be a super job!

 

[Larry (Omaha)]

In the illustration shown below, the arrow indicates the danger point for a drill or tap. If the cutting edges of drill or tap hit and catch, the drill and/or tap can easily break. You are correct in the location needing to be as shown in your illustration, any deviation would not be correct.

I assume the counterbored hole in the barrel through to the breech plug is already done for you. If so, centering in that hole gives you a perfect location for the drill/tap operations.

Just do a solid set up and go easy and it will be a super job!

Wrong on the assumption! Why would I want someone else to have all the fun? The breech plug came from Renner with the receiver. The barrel is from Rice and tapped at 3/4" x 1.5"deep. The nipple can't be pre determined as I have to clock fit the barrel to the receiver first. Once the fitting is done, with the hammer on 1/2 ****, I can locate and install the nipple.
Thanks again.
Larry

 

[Davey Boy]

Are you going to want a flat bottomed hole or is the drill bottom taper OK?

 

[Larry (Omaha)]

Are you going to want a flat bottomed hole or is the drill bottom taper OK?

The nipple is on order. When it arrives I can measure the thread length, and see if there is enough meat for full threads using a 60 deg bit. If there is not enough meat, I will punt and try grinding one of my bits to a lesser degree. I can partial pre drill with the 60 deg and then finish up with a less bevel. Full threads at the nipple is really my concern.

 

[Davey Boy]

What is the diameter of the hole that would like a flat bottom?

 

[Larry (Omaha)]

What is the diameter of the hole that would like a flat bottom?

Not sure, as I said before the nipple is on order. I need to mic the shoulder and add some wiggle room.

 

[Davey Boy]

I did a start on a drawing with a 1\2" hole bored to depth then guessed a 0 .3" outer dimension of the nipple. 135 degree drill point. If calculations were correct the nipple would have a seating distance of 0.014" .

For all intents and purposes that should be close to a flat bottom hole.

But with actual dimensions it may not be off much.

I only guessed 1\2" hole because you have to have room for a nipple wrench to fit.

 

[Capnball]

I do, plan on the drill press chuck holding the tap. How else can the tap be held in a ridged aligned position?

Drill press vise bolted to the drill press table?

 

[Larry (Omaha)]

Drill press vise bolted to the drill press table?

No sweat! My drill press vice, with lateral and longitudinal adjustment is bolted to a 3/4" wood base with sides that swallows the metal drill press table. The wood base is clamped on.