One of my colleagues mistaken something in the assembly that I designed. He was worried that we will not get it ouf of the plate if needed. So we started to talk about mounting and dismounting dowel pin. Here are some interesting points from that conversation:
Dowel pin – counter sink hole
When designing a hole for a dowel pin, the hole should always be counter sunk. When the hole is not counter sunk it is really difficult to put the pin into the hole when mounting the assembly.
Dowel pin – thinner mating pieces, through hole
If you are planning to use dowel pins such as the one in DIN 7 standard then both parts that are mated with this pin should be made with through holes. This is necessary in a case of disassembling. When both parts have through holes no matter where the pin remains after separating there will always be a way to get it out.
Dowel pin – pin with a thread
If there is a need to have one blind hole then dowel pins with threaded hole on one side would be used. This happends for example when one part has a wall too thick for a through hole. The mounting should be done so that the threaded hole is facing the part with a through hole. When disassembling if the pin remains in the part with a through hole then it can easily be tapped out. If it remains in the blind hole the threaded hole on the pin can be used to insert a screw and pry it out. There are even special tools for this like tap extractor (basically a rod with a thread on one end and a heavy cylinder that acts like a reverse hammer when slammed on the stop on the other end of the rod)
Dowel pin – alternative for disassembly
When there is no possibility to provide a through hole on either parts, one should always try to use threaded dowel pin and provide the part with a threaded side of the pin with a looser tolerance. This increases the possibility of the dowel pin remaining on the part where there is no threaded hole. This way it can be easily extracted with a thread.
I hope that this can prevent a few headaches 😉
Until next time,
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