Making Custom Threaded Inserts (3D Printing)




Introduction: Making Custom Threaded Inserts (3D Printing)

Many times when you print a downloaded part, the fastener holes or hex recesses are too tight. Other times, the type or size fastener that the design requires is just not available, which happens a lot here on Maui. The Item pictured here is a spindle bracket to replace the motor on a ShapeOko CNC router. Since the fasteners on the original machine were metric fasteners, the new bracket was designed the same. The problem was that the 3" long clamp bolts were not available at all. The through holes were of the proper size to be able to accept a length of 10-24 TPI all thread. That meant I could substitute a hand-made bolt assembly for the designed fasteners, but the recess for the nuts on the back side were too small to accept the 10-24 nuts. My solution was to double nut the threaded shaft and use heat to insert the nuts into the recess forming an insert that had a threaded shaft attached.

Step 1: Tools Required

You will need to hold the piece you are modifying while you heat the 3D-printed part and press or pull the fastener into place. I used a combination of clamps so that my long threaded rods would extend below the table.That allowed me to pull them. I used a standard hobby heat gun to heat the nuts. The heated nuts would then melt the plastic as they were being pulled. For final clean up, I used a file to remove the displaced plastic from the surface. It is also a good idea to wear safety glasses, and have heat proof gloves or a pair of vise grips to hold and pull the fastener.

Step 2: Create the Insert

You need to create a method for holding the insert and forcing it into position. Because I had a long fastener, I chose to thread two nuts onto the rod and use thread sealer to hold them with the flats aligned.

Step 3: Clamp the Part

Because you are dealing with hot parts it is necessary for everything to be fixed in place while heating and inserting the metal parts. I used the two different styles of clamps, because I did not have a bench vise.

Step 4: Heat the Insert

3D printers use filament material that is thermoforming. That means that a printed part can be reheated and reformed. Because of this you need to be very careful that you do not actually heat the printed part, or it will distort. By heating only the metal part to be inserted, it melts the plastic as it is being inserted. This causes the plastic to reform it and bond to the metal part. This creates a very strong fastener.

The metal part does not need to be heated for very long. With a 1500 watt gun, it only took about 15 seconds to get the nuts hot enough to reform the plastic.

Step 5: Form the Plastic (Pull the Insert Into Place)

Immediately after heating the metal part, pull or push it to insert it into position. Use constant slow movements to get it in its final position. Plan your movement, so you don't go too far. It is difficult to reform the material if you push to far, and in some cases, it may be impossible to correct a mistake.

Step 6: Clean Up Excess Material and Finish the Part

After the plastic has cooled you will need to remove displaced plastic. I used a hand file for this step to get good control. If you use power tools, be sure not to heat up the plastic or your inserted bolt will probably move.



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    19 Discussions

    The Metric System is the standard for measurements for most of the world. In the US it is the imperial system that is used for everyday items. In remote locations (Like Maui) you need to be able to adapt by using what you can get. I may have been able to purchase and have shipped the metric hardware to assemble it with metrics but from McMaster Carr with shipping the four screws and nuts would have cost me over $75 Unless I have someone in the "48" to reship and then it would be around $20 As it was adapted the nuts and bolts purchased individually at the local ACE were only about $7.
    The Local Hardware assortment is very limited in scope and quantities, (everything comes in on Boat or Plane). Space for storage is very expensive. Normal day to day items like Paper goods actually become non available at certain times .

    Then you need to work around the technical issues of 3D printing where holes and shapes both grow and shrink in PLA depending on the thickness and with our high humidity and temperatures in parts of the Island absorb moisture and change size after the print.

    Those are the taxes for living in paradise along with 5-7 days is fast shipping from anywhere on the mainland (that is express). There are some better Hardware stores on Oahu but you can't drive there from here

    Alternately, you could make a round hole and drop in a helicoil for the same price as the nut. The screw would press it out into the plastic and seat it nicely. It would be a lot quicker, but of course it requires you to have helicoil available when you do it.

    8 replies

    Erica If I had designed the part I would have done it in std measurements not metric. The part was already posted on Thingaverse with some good instructions for filling the voids to make it solid. They just did not give sources for the hardware. I had a problem I am currently in the middle of the North Pacific Ocean on Maui.Trying to find a 3 mm dia. 300 mm long bolt is hard on the mainland and impossible here on Maui. The connection you see is blind when the bracket is installed on the machine and the mating part cannot be placed on when it is not in place. That was the reason I chose to make a custom stud in the first place.

    I posted the method to show others a different method of getting out of a tough spot. I have 40+ years of product engineering testing experience so I do know about threaded inserts and a multitude of fastener options and I do have some of them in my personal hardware store here. I chose this one because of the multitude of challenges in the installation.

    Great Instructable Peter. Sorry, I think you are mistaken to assume that the "US Customary systems" is the standard. It might be the standard you've used or the most commonly use systems in your place of residence but outside this boundaries most countries have adopted the "Metric system" or "International System of Units"

    However I completely understand that making the change is difficult and you have to deal with maintaining legacy systems but designing new hardware that require a silos systems will inevitably create problem for the distributer of that hardware. Any modern hardware that is sold internationally should be made using the systems used by the most and not the few.

    Elmuchacho Like the weather in Maui everything is local if your designing for yourself you design with what you have or can obtain at a reasonable cost. I was in industry in the 80's when the US ried to adopt the Metric system and our politicians did not have the strength to force it onto our industries. Our global manufactures do design in metric but our Hardware stores are 40 years behind the time in stocking hardware. And here on Maui its more like 70 Like officer Friday always said "Just the Facts"

    I have tools for both and can do the work in either it's not a prejudice just a fact of life when you're in the middle of the Pacific Ocean (my decision last year)

    You mentioned in the text that the flats are aligned but the photo shows the two nuts are offset which I would have thought would provide better keying of the nuts. Is the photo correct?

    BTW We have the same problem in metric countries when we have to work in non-standard (ie. imperial) measurements :)

    The first set of nuts aligned easily the second set were offset maybe 15 degrees Manufacturing tolerances of the processes of making the nut. I could have used two wrenches to force into alignment but it was not worth the effort in this case. The engineering reason for the two nuts was so they would jam together and lock on to the threads so the threaded rod would not come loose.. After I did the first side and saw the amount of plastic that was displaced I figured that it would act as a good lock for the parts. after it cooled it proved true. The threaded rod was locked into place.

    I'm glad you reminded me that the rest of the world has the same problem it is just that they are looking through the other side of the window.

    There is another problem we as Makers have in general is that every consumer 3 D Printer and filament combination prints holes and cavities to different tolerances making methods for tweaking important unless you're going to endlessly modify and reprint the design.

    Thanks for the detailed reply.

    I know what you mean about the problem of tolerances between machines. Even the same machine has different tolerances depending of the direction of the feature (eg vertical vs horizontal).

    I ran into this trying to print close fitting parts. I ended up printing two calibration parts consisting of a matching set of five holes and five posts on bases in 0.1mm increments from 9.8mm to 10.2mm increments to see how well they matched so I could modify the real design without having to continually print different versions or hack away at the printed parts. It helped a lot.

    It was also very instructive for others that use the printer.

    Do you have experience that suggests a helicoil would work well? I am just wondering not meant to be antagonistic.

    One reason why the recessed nut is used and often works well, is because you spread the load onto a decent surface area of plastic. But a proper helicoil, if it really does set, might work OK, but it will need to be of greater threaded depth compared to the nut to have comparable strength.

    See my note to Erica it explains the problem I had in detail BTW I would have used a ROSIN insert instead f a helicoil. Helicoils are meant to repair already threaded holes that have been stripped out. I was working with a hex void so a Heilicoil of the proper size for the part would not have worked at all unless set in with epoxy.BTW 3D printers use mostly PLA and it is not an easy plastic to bond to.

    I do the same thing but I just rest a soldering iron on the nut until it starts to slide in then set it in position. I also hold the nut in position with a bolt in it only half a turn. Then when the nut warms up I quickly unscrew the bolt and flip the piece over onto a heat resistant surface and press down pushing the nut in. This aligns the nut perfectly flat.

    I use smooth rods from home depot with a drill to heat up holes in parts, Especially if you have scrap piece with a burr on it, you can use that to cut into the piece. then just slide the piece up and down the rod while running the drill, the friction alone will heat up the part and rod. This is really only good for parts that are close to the correct size though.

    Great idea and thanks for sharing! I have used a similar technique with a soldering iron to "press in" round inserts for metric screws. I think most would agree that plastic doesn't thread very well so metal inserts/nuts are often needed.

    A problem I've had using the soldering iron technique is that the part gets too hot and it is very easy to push it in too far or get it crooked. So, I'm thinking use of a heat gun might work better.

    Also, I like your idea of "re-sizing" nut recesses (rather than "Dremel" them out) when they are either too small or metric when you don't have metric. Recently, I was planning to substitute a #10 screw for a M5. The bolt diameter was fine, but, the nut wouldn't fit the M5 recess. So, I wound up chasing down M5 hardware when I could have used your technique to simply enlarge the nut recess.

    Could use something like this for a stronger bond:

    Great Idea and well written

    Love it! As I have yet to try-out 3D printing and am not very familiar with it, I assume the white "plastic" part was 3D printed ... correct?

    Very good. I like the inventive aspect.

    I've used an adjustable soldering iron for the heat source. Heat is better controlled with this method. Later the iron can be used to finesse the job. Fixturing is also very important. It frees up the hands for other matters and allow for better monitoring of the repair process.

    It would be helpful sometimes to help keep the surrounding plastic cool. This could be done by surrounding the extremities with some metal or maybe even a water bath. In the case of a metal, a little mold release on the metal surfaces in the event that the surrounding plastic becomes molten. Another reason for fixturing (part control). Remember, that in plastic injection molding of thermoplastics, the molten plastic is injected into a water cooled mold (fixture). The part can be demolded seconds after completion of the injection cycle.

    Contrary to this, a rubber component that is injected hot into a mold that is heated to around 350F where the part cures for several minutes before demolding.

    Keep up the inventiveness.