locknut for bearing preload

[M100]

Originally Posted by philbur Why would it be square. If the thread is lathe cut, yes, if you drill a hole and use a tap almost certainly not. Phil

It was intended as a rhetorical question, but in the circumstances I would have expected anyone concerned about bearing preload would have a lathe or, if they were in the back end of nowhere and latheless, have the skill to hand tap accurately.

At the end of the day, this is "benchtop mills" after all, off the shelf commercial nuts with off the shelf commercial washers will almost certainly suffice as ground end nuts will make 3/5 of 5/10th of bugger all difference

But given the choice I'd go for two slotted nuts (google DIN 1804) - Maryland Metrics http://mdmetric.com http://mdmetric.com/fastindx/ud52_54.pdf is a US supplier but they should be available from any decent bearing supplier.

[philbur]

Not really, 1/30th or less of a turn could easily be too much so you would be trying to measure very small differences in deflection. With all the trouble necessary you may as well size and make a precision spacer.

For the class of work you are doing use a standard nut, drill and tap a hole for a locking screw as per CarbideBobs suggestion. Then tighten the nut until you can measure no free play with a DTI and a hard push/pull. Check that the bearing runs freely then tighten the locking screw and you are done. Finally use the DTI to check for free play under operating load. If detected tighten the nut a touch further and recheck under load.

Is this a precision set-up, no? Is it more than good enough for your purposes, yes? Some would be unhappy and call it a compromise. They fail to understand that all engineering is a compromise. Good engineering is what gets the job done for the least time, effort and cost, anything else is over-engineered.

Phil

PS: I admit to being prone to over-engineer, but I'm constantly working to correct this.

Originally Posted by lagfish Can you also not experimentally determine the preload? For example: Get a precision spring of a known K value, and place it in between the two bearings you're using and on the same ballscrew. Using the K value figure out how much deflection of the spring you need for the preload you want. Tighten the nut with a torque wrench until the desired deflection on the spring is reached. Note the amount of torque needed, and this should be the amount of torque needed to preload it on the real bearing block

[lagfish]

Thanks everybody for your input