Make a Large dia precision spindle using engine bearing inserts...with no scraping ?
I have read and studied and read and underlined and studied Harpit Sandu's wonderfull book "Spindles" for years, and in my mind slowly worked through every step to construct each spindle......
However what I would like to make is a very large dia precision hollow spindle... a little over 4" hole. In am thinking of plain bearings, and thinking of using bearing inserts from a large truck engine , and attempting to get away without scraping .....
How reasonable does this sound? I am thinking with this setup the runout would be porportional to the degree of circularity of the OD of the spindle journals and by grinding it between dead centers could be kept very low...perhaps half a tenth ?
Perhaps the engine block itself could be used for the housing , simplifying things a bit.
Last edited by lalatheman; 02-17-2017 at 11:31 AM.
I doubt you would find 5" or 6" bearings on a truck engine, more like 3" max.
lalatheman: I'm curious, what is the nature of your spindle. How fast does it need to turn? How much load does it expect to carry? Large roll grinders use two point babbit blocks for bearings that carry the weight of the rolls. These rolls weigh tons.
Maybe from a marine engine?
so the plan is to somehow get the appropriately sized engine bearings (new or used?) and grind the spindle to fit? could work.....scraping them isn't that extremely difficult though....might let you use used ones (new may be very expensive)
So curiosity - what are doing that needs a slow speed large bore spindle good to 1/2 a tenth?
Crank to shell clearances (for oil and temperature) are large in comparison to precision tapered bearing typically used in lathes. You could get them adjusted down (grinding down the main bearing retainers or increasing the spindle size), but there are limits. Pressure oil feed required also. You will need to add a method to adjust pre-load.
I wouldn't hand scrape the spindle - standard crank grind setup (even use you local engine re-builder) will work to 10ths with care. Measuring sub-10th's? hmmm..
A used "oil industry" big bore lathe might be the way to go.
Last edited by lakeside53; 02-17-2017 at 01:14 PM.
The need for constant pressurized oil feed on such bearings makes using the block sound interesting. But that would end up being a rather LONG spindle. And there's the issue that the main oil delivery gallery in the engine block is often near the middle of the crank and oil delivery to the end journals relies on the holes drilled in the crank. So you might find that your own housing is a better idea.
I too boggle at the idea of such a spindle other than in a rather large lathe. And when we start looking at lathe spindles that will see large side and end loads supported by plain bearings we need to look at the surface area of the bearings and the determining if the oil film will withstand the loads without breaking down and allowing metal to metal contact. The study and focus on that oil film issue and determining the optimum clearance needed to allow for the oil film is a basic but important calculation in any engine design.
3406 Caterpillar engine shows a 4.750 main diameter.
Not sure what you are trying to design and make, does not look like you have a machine in mind.
Regardless of that the plain bearings look like a good choice. In my compressor designs I am using 4", 5" and 6.25" bearing bores. The bearings are not plain bushings, they have several hydrodynamic ramps to provide a shaft lift at operational speed. There is a clearance between bearing bore and a shaft journal, it is around several mills on a diameter.
If your spindle rotates very slow, you will not need hydrodynamic bearings - they will be useless. Plain bushing with reduced clearance may work, but you have to watch it - it may seize on the shaft due to thermal variations. We use aluminum based bearing alloy. It works like a poor man's babbitt.
To produce a big diameter precision journals on the 4" ID spindle is not easy. You must prepare the spindle centers to make them as round as your journals supposed to be or better. Otherwise the journal OD will just repeat the shape of the center chamfer. The best way to make round centers is to lap them. I hope you have access to a big cylindrical grinder and have big dead centers.
the scraping is done to the bearing ID, to bring them into a perfect fit with the shaft. (whole thing is the spindle, rotating part is the shaft afaik).
Originally Posted by lakeside53