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Machine Shop Practice: Making Custom Metal Hardware For Basses
- Thread starter Bruce Johnson
- Start date
I dunno, it took off a lot of metal pretty quickly. He just hadn't figured that electricity doesn't care which metal it takes off.Once again, Forrest Gump's mom was right.
If you ever try sawing stainless steel on your wood-cutting bandsaw, you'll get a smaller version of that plasma sawing. Seriously. The teeth will turn red hot and strip off. Long shower of sparks under the table. If you keep going, the red hot edge of the band will sort of grind away at the stainless. Until the band breaks. Or the bandsaw catches fire. I don't recommend it.
If you have a drill press with a foot switch that reverse spindle rotation, use that.
When the tap grips into the metal, let go of the lever.
When the tap has gone through the metal, but before it lost the thread, stomp on the foot switch and let the tap reverse it's way out of the hole.
Do NOT use this method if the hole isn't through the metal piece, i.e. has a bottom.
When the tap grips into the metal, let go of the lever.
When the tap has gone through the metal, but before it lost the thread, stomp on the foot switch and let the tap reverse it's way out of the hole.
Do NOT use this method if the hole isn't through the metal piece, i.e. has a bottom.
Okay, back to the method of tapping holes; cutting threads in small metal parts.
I'll talk about:
These are the basic tools for hand tapping threads in small parts, like bridge parts for a bass.
In the center is the tap itself. As we discussed in a previous post, there are different types of taps available. For small aluminum and brass parts, I recommend that you get a good quality 2-flute Spiral Point Tap, sometimes called a Gun Tap. Buy the specific sizes you need. They are made to tap many thousands of holes in steel. With some care, they will last you decades in a small shop. Worth the investment. This is a 10-32 Spiral Point Tap; McMasters calls them Chip-Clearing Taps For Through Holes; $7.78 each.
I show two styles of tap handles, a T-handle on the right and a small straight handle on top. They are both handy to have.
On the left is a small cup (spray can lid) with some Tapping Oil in it. Tapping oil is available in small squeeze bottles. It's a blend of cutting oil made specially for...tapping. You can use regular oil in a pinch, but Tapping Oil does work better.
At the bottom is a small scrap of 3/8" square 6061 aluminum bar stock, with a #21 pilot hole drilled in it. There are charts everywhere specifying the Tap Drill sizes to use for each particular thread size. #21 is standard for a US 10-32 thread. Look up the size you need for the tap you buy, and get a Screw Machine Drill of that size. Get the correct size, don't substitute something close.
To tap small parts like this, I usually like to clamp them in the vise like this, with the hole going horizontally. And I use the small T-handle Tap Handle.
Dip the tip of the tap into the Tapping Oil.....
And start threading the tap into the hole. Go by eye to keep the tap horizontal and lined up square to the hole. You can feel, as it starts cutting, that it will tend to pull itself in line with the hole. Just start turning it in. Continue turning it in, no need to stop or back up. That's for those silly General Purpose Taps. Spiral Point Taps don't need or want to have the chips broken up....
...Because they cut the aluminum as a string chip, coiling it and pushing it out the other side. Tapping a blind hole, the chip is coiled up and smashed down into the bottom of the hole. You use a small hook to pull it out.
If you prefer, you can clamp the block in the vise and tap the hole vertically. This works best with the classic flat tap handle. It's fairly easy to gauge the handle being level all around, to get the tap started square. Same technique: Turn it all the way down through in one continuous motion, until the straight part of the tap is through the other side. You'll feel the turning torque get much lighter. Stop and turn it backward, threading it all the way out. You are done!
Next up, I'll show Hand Tapping Machines, and Power Tapping Machines! For increased accuracy and speed! But hand tapping like I've shown above works fine for most small batches of custom bass parts.
I'll talk about:
- Hand tapping
- Hand tapping with a Hand Tapping Machine
- Power tapping
These are the basic tools for hand tapping threads in small parts, like bridge parts for a bass.
In the center is the tap itself. As we discussed in a previous post, there are different types of taps available. For small aluminum and brass parts, I recommend that you get a good quality 2-flute Spiral Point Tap, sometimes called a Gun Tap. Buy the specific sizes you need. They are made to tap many thousands of holes in steel. With some care, they will last you decades in a small shop. Worth the investment. This is a 10-32 Spiral Point Tap; McMasters calls them Chip-Clearing Taps For Through Holes; $7.78 each.
I show two styles of tap handles, a T-handle on the right and a small straight handle on top. They are both handy to have.
On the left is a small cup (spray can lid) with some Tapping Oil in it. Tapping oil is available in small squeeze bottles. It's a blend of cutting oil made specially for...tapping. You can use regular oil in a pinch, but Tapping Oil does work better.
At the bottom is a small scrap of 3/8" square 6061 aluminum bar stock, with a #21 pilot hole drilled in it. There are charts everywhere specifying the Tap Drill sizes to use for each particular thread size. #21 is standard for a US 10-32 thread. Look up the size you need for the tap you buy, and get a Screw Machine Drill of that size. Get the correct size, don't substitute something close.
To tap small parts like this, I usually like to clamp them in the vise like this, with the hole going horizontally. And I use the small T-handle Tap Handle.
Dip the tip of the tap into the Tapping Oil.....
And start threading the tap into the hole. Go by eye to keep the tap horizontal and lined up square to the hole. You can feel, as it starts cutting, that it will tend to pull itself in line with the hole. Just start turning it in. Continue turning it in, no need to stop or back up. That's for those silly General Purpose Taps. Spiral Point Taps don't need or want to have the chips broken up....
...Because they cut the aluminum as a string chip, coiling it and pushing it out the other side. Tapping a blind hole, the chip is coiled up and smashed down into the bottom of the hole. You use a small hook to pull it out.
If you prefer, you can clamp the block in the vise and tap the hole vertically. This works best with the classic flat tap handle. It's fairly easy to gauge the handle being level all around, to get the tap started square. Same technique: Turn it all the way down through in one continuous motion, until the straight part of the tap is through the other side. You'll feel the turning torque get much lighter. Stop and turn it backward, threading it all the way out. You are done!
Next up, I'll show Hand Tapping Machines, and Power Tapping Machines! For increased accuracy and speed! But hand tapping like I've shown above works fine for most small batches of custom bass parts.
Continuing on with tapping technique:
On some parts, it's very important to make the tapped holes accurately square and perpendicular to the part. For example, the two jacking screws on my Scroll Bass bridges.
I found out by experience that, if those two threaded holes weren't tapped accurately square, the bridge would sit crooked on the bass and look terrible. I ruined several bridges learning that lesson.
To help you tap your holes nice and square, they sell machines like this. This is called a Hand Tapping Machine. It's pretty simple. A vertical spindle riding in bronze bushings, a cast iron C-frame, and a flat table with some sliding holding jaws. The tap goes in the chuck on the end of the spindle, and you turn it by hand with the big crank on top.
These aren't expensive and they work quite well. I bought this one many years ago when I first had the problem with the jacking screw holes. This machine solved the problem. I used it for many years just for tapping the 1/4-20 holes in my bridges.
Until......
...My friend Thomas gave me this monster. It's a custom made Hand Tapping Machine. Same function as the one above, but bigger and heavier. It's all welded steel and weighs about 300 lbs. It works beautifully.
It was given to Thomas by a friend who was retiring and closing up a machine shop. Thomas had it outside the building here, covered with a tarp, for about five years. He didn't know what to do with it, and offered it to me. Of course, I took it in and gave it a good home. It's a nice machine.
Kind of overkill for tapping my little bridges, but hey. I think it was built for tapping automotive cylinder heads, judging by the size? Thomas comes down and uses it now and then.
So, now it gets the job of tapping the jacking screw holes in my bridges. And many other tapping jobs. Particularly larger size holes in small or fragile parts.
The tap is turned by hand by the crank up top.
Now, if you don't happen to have one of those Hand Tapping Machines nearby, you can use your drill press to hand tap small holes, and get them square. Clamp the tap in the chuck, and the part in your drill press vise (with its step jaws). Then with the motor shut off, turn the tap down into the part. Rotating the drill chuck with your hand.
That works, for small sizes.
And then there's Power Tapping. Not necessary for most small shops. Only if you tap a lot of holes, like I do. Power Tapping is done with a drill press fitted with a special device called a Tapping Head. This thing will tap a hole in about 2 seconds.
Tapping Heads are made by a few different companies, but the most popular are Procurnier brand. This is a Procunier #1 head. A new one costs about $800. I bought this old Craftsman drill press, fitted with the Procunier #1 Tapping Head, for $120 on an ebay machinery auction. I keep it set up with a 10-32 tap, and do all my neck bars, body bars and truss rod parts with it. I've power tapped many thousands of holes with it over the years. The drill press itself is getting worn out, but the Procurnier head is still going strong.
I have this second power tapping drill press, a small import drill press also fitted with a Procunier #1 head. I bought it on auction for $100. I keep it set up with a 6-32 tap, for all my bridge saddles.
These Tapping Heads are complex little machines. It's two clutches and a planetary gear set. When you start the drill press motor, with no pressure applied to the tap, the head is in neutral. The tap isn't being driven and just spins freely. Pull the quill handle, bringing the tap down into contact with the part, and the forward clutch engages, which connects the tap to the spindle. The drill press motor drives the tap down into the part. As soon as you let up on the pressure on the quill handle, it goes into neutral again, and the tap stops turning. Then, lift up lightly on the quill handle, and the reverse clutch engages, which drives the tap in reverse, at double speed. It zips back up out of the hole. The whole cycle takes about 2 seconds.
Tapping heads are used in factories to tap a lot of holes quickly.
Thomas also gave me this: A #2 Procunier Tapping Head. A #1 head will do up to 1/4" taps; this #2 head is good up to 1/2" taps. It has an MT2 arbor, and I should be able to couple it up to my big Royersford drill press. For some heavy duty power tapping fun! I haven't tried it yet.
I have three other giant old drill presses in my machinery room, waiting for repairs and restoration. I may eventually fit this #2 Procunier head up to one of them.
That's about it for tapping technique. Go ahead and ask any questions.
On some parts, it's very important to make the tapped holes accurately square and perpendicular to the part. For example, the two jacking screws on my Scroll Bass bridges.
I found out by experience that, if those two threaded holes weren't tapped accurately square, the bridge would sit crooked on the bass and look terrible. I ruined several bridges learning that lesson.
To help you tap your holes nice and square, they sell machines like this. This is called a Hand Tapping Machine. It's pretty simple. A vertical spindle riding in bronze bushings, a cast iron C-frame, and a flat table with some sliding holding jaws. The tap goes in the chuck on the end of the spindle, and you turn it by hand with the big crank on top.
These aren't expensive and they work quite well. I bought this one many years ago when I first had the problem with the jacking screw holes. This machine solved the problem. I used it for many years just for tapping the 1/4-20 holes in my bridges.
Until......
...My friend Thomas gave me this monster. It's a custom made Hand Tapping Machine. Same function as the one above, but bigger and heavier. It's all welded steel and weighs about 300 lbs. It works beautifully.
It was given to Thomas by a friend who was retiring and closing up a machine shop. Thomas had it outside the building here, covered with a tarp, for about five years. He didn't know what to do with it, and offered it to me. Of course, I took it in and gave it a good home. It's a nice machine.
Kind of overkill for tapping my little bridges, but hey. I think it was built for tapping automotive cylinder heads, judging by the size? Thomas comes down and uses it now and then.
So, now it gets the job of tapping the jacking screw holes in my bridges. And many other tapping jobs. Particularly larger size holes in small or fragile parts.
The tap is turned by hand by the crank up top.
Now, if you don't happen to have one of those Hand Tapping Machines nearby, you can use your drill press to hand tap small holes, and get them square. Clamp the tap in the chuck, and the part in your drill press vise (with its step jaws). Then with the motor shut off, turn the tap down into the part. Rotating the drill chuck with your hand.
That works, for small sizes.
And then there's Power Tapping. Not necessary for most small shops. Only if you tap a lot of holes, like I do. Power Tapping is done with a drill press fitted with a special device called a Tapping Head. This thing will tap a hole in about 2 seconds.
Tapping Heads are made by a few different companies, but the most popular are Procurnier brand. This is a Procunier #1 head. A new one costs about $800. I bought this old Craftsman drill press, fitted with the Procunier #1 Tapping Head, for $120 on an ebay machinery auction. I keep it set up with a 10-32 tap, and do all my neck bars, body bars and truss rod parts with it. I've power tapped many thousands of holes with it over the years. The drill press itself is getting worn out, but the Procurnier head is still going strong.
I have this second power tapping drill press, a small import drill press also fitted with a Procunier #1 head. I bought it on auction for $100. I keep it set up with a 6-32 tap, for all my bridge saddles.
These Tapping Heads are complex little machines. It's two clutches and a planetary gear set. When you start the drill press motor, with no pressure applied to the tap, the head is in neutral. The tap isn't being driven and just spins freely. Pull the quill handle, bringing the tap down into contact with the part, and the forward clutch engages, which connects the tap to the spindle. The drill press motor drives the tap down into the part. As soon as you let up on the pressure on the quill handle, it goes into neutral again, and the tap stops turning. Then, lift up lightly on the quill handle, and the reverse clutch engages, which drives the tap in reverse, at double speed. It zips back up out of the hole. The whole cycle takes about 2 seconds.
Tapping heads are used in factories to tap a lot of holes quickly.
Thomas also gave me this: A #2 Procunier Tapping Head. A #1 head will do up to 1/4" taps; this #2 head is good up to 1/2" taps. It has an MT2 arbor, and I should be able to couple it up to my big Royersford drill press. For some heavy duty power tapping fun! I haven't tried it yet.
I have three other giant old drill presses in my machinery room, waiting for repairs and restoration. I may eventually fit this #2 Procunier head up to one of them.
That's about it for tapping technique. Go ahead and ask any questions.
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Great stuff. I had no idea there was such a thing as a tapping head. Thanks Bruce!
I'd known *about* them but the explanations I'd gotten about how they worked were deep in the weeds and I didn't really learn anything. I got a lot more out of the minute I spent reading Bruce's post.
Another note about the power tapping heads, if you are interested:
My two #1 Procunier heads are the style that clamps directly to the housing of the drill press. They have a special arbor inside with a MT1 taper, that fits up into the drill press' spindle. They are intended to be semi-permanently mounted to a drill press. You have to make sure you get the right size to fit the drill press you fit it to.
However, they also make versions which have a straight 1/2" dia input shaft. You can clamp that right into the chuck of your drill press. The housing of the tapping head floats freely, and there's a long horizontal rod that sticks out and contacts the drill press column, to keep the housing from spinning. One of those tapping heads can be installed on your existing drill press in a minute, used for a while, and then taken off and put away. For occasional use.
Keep your eyes open for one of those for cheap on ebay or Craigslist. Procunier is the leading brand, but Tapmatic, Jarvis, and several other companies make them.
Also, beware that most tapping heads require special collets, different sizes to hold the different size taps. The Procunier collets are, like, $35 each. Available, but not cheap. If you are buying a used tapping head, check to see how many collets come with it.
My two #1 Procunier heads are the style that clamps directly to the housing of the drill press. They have a special arbor inside with a MT1 taper, that fits up into the drill press' spindle. They are intended to be semi-permanently mounted to a drill press. You have to make sure you get the right size to fit the drill press you fit it to.
However, they also make versions which have a straight 1/2" dia input shaft. You can clamp that right into the chuck of your drill press. The housing of the tapping head floats freely, and there's a long horizontal rod that sticks out and contacts the drill press column, to keep the housing from spinning. One of those tapping heads can be installed on your existing drill press in a minute, used for a while, and then taken off and put away. For occasional use.
Keep your eyes open for one of those for cheap on ebay or Craigslist. Procunier is the leading brand, but Tapmatic, Jarvis, and several other companies make them.
Also, beware that most tapping heads require special collets, different sizes to hold the different size taps. The Procunier collets are, like, $35 each. Available, but not cheap. If you are buying a used tapping head, check to see how many collets come with it.
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Here's some recent power tapping in action. Yes, I actually use my cool machines and procedures!
A batch of 50 aluminum bridge saddles, for a batch of 12 replacement bridges for vintage Ampeg Scroll Basses. Hand tapping 50 little parts gets tedious.....
So I power tapped the 6-32 holes in them using my small drill press with the Procunier tapping head. Drill press vise with the stepped jaws. According to my shop logbook, it took 20 minutes total to power tap the 50 saddles.
That's what power tapping is for. If you are just making 4 saddles for one custom bridge, hand tapping is fine. But hand tapping 50 saddles is annoying.
A batch of 50 aluminum bridge saddles, for a batch of 12 replacement bridges for vintage Ampeg Scroll Basses. Hand tapping 50 little parts gets tedious.....
So I power tapped the 6-32 holes in them using my small drill press with the Procunier tapping head. Drill press vise with the stepped jaws. According to my shop logbook, it took 20 minutes total to power tap the 50 saddles.
That's what power tapping is for. If you are just making 4 saddles for one custom bridge, hand tapping is fine. But hand tapping 50 saddles is annoying.
Sorry if you said this already and I missed it (there's a lot to take in here) what rpm range is good for power tapping? Is Rapid Tap or similar ok or is a milling coolant necessary?
Both of my power tapping drill presses are set on the lowest speed of the pulleys, about 400-500 rpm. I find that to be a comfortable speed for power tapping 6-32 and 10-32 holes in aluminum and brass. I'm sure that you could go faster if you wanted to, but I prefer to keep it at a reasonable rate. Because of the reaction time on when to lift up on the quill handle.
These tapping heads also have a safety feature. You can adjust the release torque of the clutch. If the tap jams or hits bottom, the clutch will slip before it breaks the tap. You can add some safety margin by loosening the V-belt tension on the drill press.
Yes, Rapid Tap is one of the standard brands of tapping fluid.
@Bruce Johnson do you ever spot your hole deep enough to give you a slight chamfer after you drill?
also, why not tap the holes why you already have the part positioned in the mill? Put the spindle in neutral and hand tap it…(or power tap it if your feeling bold) I’m sure it’s much faster with the power tapping, but I was taught to do as many operations in one position as possible before moving a part.
this thread has been a great read! I look forward to any future additions.
also, why not tap the holes why you already have the part positioned in the mill? Put the spindle in neutral and hand tap it…(or power tap it if your feeling bold) I’m sure it’s much faster with the power tapping, but I was taught to do as many operations in one position as possible before moving a part.
this thread has been a great read! I look forward to any future additions.
In production, you'd have a lot of time lost changing from drill to tap and back to drill if you tap every hole while the part is clamped from drilling it. Perhaps not bad for one part, but a real impact on 20 or 50 parts.
Now, if you happen to be working the part on a turret lathe, that changes things, as tooling changes are a matter of seconds, but that's not a common situation for most general purpose shops.
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Hello Wilbursaurus; You sound like a ferocious creature!
Yes, sometimes I'll drill the spot larger than the diameter of the hole, which leaves a small chamfer afterward. On little holes. But on soft metals, I'll usually have to touch a countersink in them anyway, to clear out a small lip from the drilling.
Yes, you can hand tap a hole right in the milling machine, right after drilling. I'll sometimes do that if I'm making a one-off part that needs higher accuracy. Like tool & die work or a part for a machine. For most bass hardware, I'm making batches of parts with multiple tapped holes. It would slow things down too much to be changing from drill to tap at every position. I drill all the holes in the whole batch, then walk a few steps to the drill press with the tapping head.
It sounds like you've had machinist training and experience? You're welcome to add knowledge and tricks to this thread.
I got real busy through the fall on other projects and subjects here on TalkBass. But I do intend to continue on with this thread. Plenty of other simple metalworking techniques to discuss.
good to hear you intend to keep adding to it!
It’s been helpful because all my training has been in a machining environment. I literally have a teacher that says “well you could do it that way or the right way” when I work on some projects. What he usually means is “that would work but…”. Edgefinders and indicators are generally the starting point for me, So a lot of these alternative techniques are new and refreshing
as a side note, even as a younger guy, it’s sad to see this kind of knowledge fading out. It so useful in understanding what it is we are doing! I feel dependence on CAM/CNC software has replaced a lot of this instead of becoming a very useful extension of it.
So long as you can get a copy of Machinery's Handbook it shouldn't fade too far out. Mine is the 19th edition, so 1971, but still chock-full of useful information.
A Gerstner toolbox even has a particular drawer for it...
A Gerstner toolbox even has a particular drawer for it...
Ooops. My reference material may be a little out of date.
Nope, just classical. And may have a lot of info about using shapers that you'll have to rescue one to apply.
