Picture of Make an Acme Tap
In this article I will describe how I made myself an acme tap for tapping soft materials.
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Step 1: Fabricate Guide Blocks

Picture of Fabricate Guide Blocks
The first item I made for this project was a pair of guide blocks to hold the threaded rod stock with. I made mine uniform, and square, then drilled holes out of the center of each. I used some phenolic cellulose material I had on hand, I am sure other materials are equally as suitable to use.

Step 2: Add Set Screws to Guide Blocks

Picture of Add Set Screws to Guide Blocks
I want my guide blocks to remain fixed on my threaded rod stock so I tapped holes for set screws into the sides of them. I took this picture at the end just so I would have an image for this step. That is why one block is already cut in half in it. I'll be getting to that shortly. Tap your blocks now. The set screws you use must be flush below the block faces when tightened onto your rod stock.

Step 3: Machine One Block as the Front Half Block

Picture of Machine One Block as the Front Half Block
The front block will need to be partially cut away to allow access for grinding to take place on the threaded rod material. I chose to perform this step on my table saw with a fence and the blade tipped to 45 degrees. I'm sure other methods would be equally as effective. This image was staged after the project was completed just so I had a picture to include for this article. It is probably a good idea to perform this operation with the set screws removed if you are going to use a power tool.

Step 4: Prepare Threaded Rod Stock

Picture of Prepare Threaded Rod Stock
Taps have a lead in chamfer on the end of them to help get the tap started. I ground mine by chucking the rod into a cordless drill then running it on a belt sander. When doing this it helps to feed into the motion of the machine. Doing so draws the work into the tool and yields more even results with less skipping of the workpiece. I'll draw a simple graphic to explain.
Snidely704488 months ago

An angle grinder might work to cut the grooves. They wear down pretty quickly, but I've never heard of one coming apart.

pfred2 (author)  Snidely704488 months ago

What wears down quickly and does not come apart? You can try to cut the gullets by hand, but I doubt you are going to get very even grinds that way. It is fairly critical that the tap be symmetrical in form in order to function properly in use.

mwoodworth22 years ago
Grinding on the side of a grinding wheel is really dangerous because it can cause the wheel to shatter and send shards everywhere.
pfred2 (author)  mwoodworth22 years ago
I've heard that. I've never seen it happen though. Perhaps it happens if a wheel is severely undercut? That I could see happening, so try to keep the wear even is the best advise I can give. That grinder has a shield on it so even if the wheel did break on it, which is not going to happen, it is not going to go all over the place. Some grinding wheels are even designed to be used on their flat faces. I have a couple of those. They are not a whole lot different than plain grinding wheels.
rimar20003 years ago
Interesting your device, pfred2. I have done some of these taps, but in a improvised way, with only one longitudinal channel. As the tap was used on wood, it worked. Never I tried to thread soft metals (alum, copper, etc) with it.
pfred2 (author)  rimar20003 years ago
I need mine to thread plastic but I am thinking about making another and trying to harden it.