Cutting Bolts Without Damaging the Threads




Introduction: Cutting Bolts Without Damaging the Threads

Every once in a while, whatever project you're working on requires a machine screw or bolt that is in between the sizes you have, meaning that you have to cut it to length. Ugh! If you clamp it in a vise, you can damage the threads. If you use a bolt cutter, you leave a double angle end that is difficult to thread into something, and sharp! Well, I came up with a simple way to cut your machine screw or bolt to the right length without damaging the threads. Just follow the steps below.

Step 1: Determine the Correct Length

For the project I was working on, the original machine screw was too short. My choices were a 3/4" or a 1 1/2", but I needed one that was 1" long. What to do?

Step 2: Tools Needed

To cut my machine screw to the right length, I'm going to use some scrap wood and some simple tools. You'll need a saw (hand or power) to cut the scrap wood, a hack saw to cut the machine screw, a drill/driver (corded or battery), pliers and a vise or clamps to hold the wood. Let's get started!

Step 3: Prepping the Wood

I know the length of the machine screw needs to be 1" long, so I measure my piece of scrap wood and cut it at 1". To secure the machine screw, I drill a hole in the face of the wood (NOT the 1" side) using a drill bit that is one size smaller than the machine screw. Time to cut!

Step 4: Get Cuttin'

Mount the wood piece into a vise (or, use clamps if you don't have a vise). Using the drill/driver, slowly drive the machine screw through the drilled hole until the head of the machine screw comes flush with the wood face. Be careful not to drive it deeper, or you'll shorten your cut length.

Step 5: Cut and Done

Using the hack saw (which has a blade meant for cutting metal), hold it flush against the wood and carefully move the saw back and forth, cutting the machine screw. As the metal gets hot from friction, and I want to make a "clean" cut, I hold the screw end with pliers. There you have it! Your machine screw or bolt is now cut to the exact size you need, and the threads are neat and clean!



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23 Discussions

This would be especially handy if I were cutting several bolts at once by drilling several holes in succession, minding the gap needed for the bolt heads. Good idea if you don't have extra nuts available or the bolt is so small you can't hold it while cutting it.

It is usually easier to find a nut or two the same size as the bolt, and run them both (2 works better as you can jamb one nut against the other) up past the length you want, then adjust the outside one back to the desired length and tighten one nut against the other. You cut the bolt using a vise or whatever, and then you have the nut to back off so that any damaged threads can be chased back into place. I sometimes run the nuts further up the threads following the cut and grind the bolt flat on the end with a small chamfer to enable the threads to start easier.


Tip 7 months ago

Maybe I'm just backwards, but I clamp the piece being cut off, where possible, so the thread damage is on the discarded piece :)

And I also spin a nut or two on first to act as a die, to recut the thread after being mauled with a saw.

I have used 2 appropriate sized nuts on the screw that is too long. I tighten them down to stabilize the screw better and put the nuts in a vise and cut off the desired amount. I often will need to dress the cut end of the screw slightly and will use a delicate file or a belt sander depending on the size of the screw/bolt.


7 months ago

What has always worked for me is to use a Dremel tool with a metal cut off wheel to cut the bolt and then use a diamond wheel to clean up any jagged or raw edges. This leaves a nice, clean and safe cut end.

2 replies

I've used the Dremel tool many times on applications similar to this, but using a power tool is no different than cutting by hand - if you have a slight tilt when cutting, you can damage the threads. That's why this method, keeping the hack saw blade flush with the wood, prevents that. Thanks for the comment!

I guess that the only "right way" to cut a bolt is the way that works for you. I have noticed that there is a number of "right ways" to cut a bolt in the comments here. I like the diversity of ideas I find here in Instructables. Well done to author and commenters alike.

Nah . Clamp in vice on the thread that will be removed. Use a thin cut off wheel in your grinder and cut through round cut end on grinder lightly

Thanks for sharing! This will really come in handy. I haven't had a chance to try it yet, but I wonder if you have any problems with the needle nose pliers damaging the threads? If so, maybe you could hold the head of the bolt stationary with a screw driver or wrench (depending on the type of bolt)?

1 reply

Thanks! The needle nose pliers are used to hold the cut-off part, so there's no need to worry about damaging the threads. Just keeps from getting warm fingers.

I **just** got through cutting a few bolts to length. What I do is run two nuts up the threads to where I need to make the cut. I jam the top nut down on the bottom cut to lock it in place. I tighten that - the nuts - in a vase and make my cut right up against the bottom nut on the waste side. This way, you can run the nuts back off to help rethread any threads that get damaged.

3 replies

Thanks for your comment. I've also used this method many times when I have just one or a few machine screws or bolts to cut. Just as effective.

This is how I do as well, and it's very effective.

That's how I've always done it. I use a cutting disk on angle grinder. 10 seconds ands it's done

a neat solution, if I was cutting down a lot of bolts I'd give this a go, but I've never gone wrong slipping on a nut to the side of the bolt I want to keep, cutting, then when you undo the nut it tidies up any mishaping of the thread. so if i were following your method I think I'd still incorporate a nut on the template somewhere, perhaps mounted in the wood, or simply sitting up near the bolthead.

1 reply

Thanks for the comment. Yes, if I were only cutting down a few machine screws or bolts, I'd just thread on a nut, clamp and cut. For doing several, this just worked out better for me, so I wanted to share with others.