What bolt thread to use for a bearing extraction drawbar tool.

[richardmorgan1]

Hi all, I've finalised the design for a KTM motorcycle swingarm bearing extraction and installation tool. I need to know which is better to use as a drawbar, fine pitch or coarse pitch bolt. I will be using a grade 10.9 M16 bolt. The most important factor is resistance to thread stripping. My initial reseach on the web suggests that a coarse thread has the greater resistance to stripping. I realise that a fine pitch would offer more force for a given ammount of turn, but the resistance to thread stripping is more important in my design. Your thoughts and comments would be greatly appreciated.

Regards Richard

 

[MintJulep]

Acme.

 

[tbuelna]

richardmorgan1-

Your swingarm bearing OD should not have a huge interference fit, so the M16 x 1.5 thread should work OK. The gr. 10.9 bolt has a hardness of approx. Rc32, which should be fairly durable for this application. But if you want an even harder material then see if you can find a gr. 12.9 bolt, which is about Rc39 hardness. Personally, I would use the fine pitch thread since it would allow slightly more precision in the application of installation/extraction force on the bearing.

As long as your drawbar design has a sufficient engaged thread length and the threads have decent precision/fit, then the threads will likely fail due to surface galling long before they fail in root shear (or "strip out"). To minimize galling use hard materials for both of the threaded components, make sure the thread fits are precise, make sure the thread flanks have a polished surface and are free from burrs or raised material, and use some sort of DFL or anti-seize on the threads. It would also be helpful to make sure your drawbar tool is designed to maintain alignment between the jack screw axis and the bearing/bore axis, so that the jack screw is not subject to eccentric loading or bending.

Hope that helps.
Terry

 

[richardmorgan1]

Many thanks for replies. I would have liked to have used a grade 12.9 but they are not readily available in the size of bolt I was after M16 x 130mm. The original design of the tool can be seen in these two you tube videos:

[url=http://www.youtube.com/watch?v=8Yjpy8dvR58]

 

[CoryPad]

Fastenal stocks M16 PC 12.9 socket head cap screws.

 

[ivymike]

When I've used big bolts for bearing pullers in the past (in particular to remove bronze bushings from skid steer buckets and arms) I used coarse-thread ones available at the local hardware store. I lubed them thoroughly w/"high pressure" grease, also from the auto parts store. After replacing a full set of bushings the bolts were looking pretty ugly - but who cares, they were only $5.

 

[ivymike]

heheh...watched the first video - that bearing was a breeze to get out compared to the bushings on the skid steer. In that instance I used 1-1/4" * 7 TPI bolts, plus a 6' cheater bar in my hands with my pickup truck helping to hold the part in place. It was a long and sweaty job.