Insane Hydraulics
Bold and audacious blog about fluid power
In this post, I want to showcase an idea for a DIY extractor for pulling bushings out of blind bores. (The DIY term is pretty relative here because you do need a lathe to make this tool).
While most of the times, when you need to pull something out of a blind bore, be it a bushing or a bearing, you can (and should ) use a "normal" extractor, when you work on the likes of Commercial gear pumps - bushings are often so notoriously tight that "normal" extractors tend to fail.
For example, this is a pretty decent kit:
But if you use a small extractor from it to pull out a bushing from a P315 gear pump, you end up with one of the "petals" bent out of shape and the bushing still in place:
Obviously, there are better (thicker) extractor tools you can buy, and you can also remove the bushing either by rolling it in at the seam or cutting it with a high sped rotary tool, but I believe that the extractor that I describe below has the right to exist, and the idea is pretty neat as well.
It fits one size only, but it is very fast and easy to work with, which is something you appreciate when you need to remove, say, eight equal bushings in a row because you are overhauling a tandem pump. Plus it relies on a common metric thread rod for doing the pulling, which means that you can easily replace it when it wears down. I can tell you that the 8.8 M14 rod that I use in the video, coupled with a standard M14 nut, is "good" for about 10-20 bushings if you run the nut always in the same spot. Of course, you can use a better rod or a thicker nut to mitigate this, or anything else that your imagination tells you, really, so don't concentrate too much of your attention on this particular execution, look at "the bigger picture".
And please, consider this post not as a description of the "best bushing extracting tool in the world", but rather as "another way to skin a cat".
It is very simple. You machine a standard circular brim extractor piece out of suitable steel (I used a scrapped cylinder rod) with the external diameter equal to the internal diameter of the bushing that you need to pull out, then run a threaded hole through the center, and then cut it in three pieces with an angle grinder using a thin (1.2 mm) disk. You will also need to grind down the brim corners on one of the three pieces for easier insertion. The idea is that you insert the three pieces inside the bushing one by one, and then use a threaded rod to pull the bushing out. The rod will be grabbing the pieces while preventing them from closing in, and the brim will never slip, no matter how hard you pull it.
This would be the extractor piece for a P315 Commercial gear pump, that uses 24x27mm bushings.
I also took an M20 nut and drilled it out to 24 mm to hold the three pieces together. The best way to showcase a DIY tool is, of course, a video, so here it goes. It is self-explanatory: