We will be sending some parts out to vendors for fabrication for the first time and I am wondering how teams typically handle the mounting holes for hex bearings.
We have had various experiences in the past - either to lose or too tight.
Last year - we bought an annular cutter and we bored the holes ourselves on the mill and they were perfect.
This year we don’t have access to the shop so we have to outsource.
I am wondering what dimensions and tolerances you use on drawings for the following machining processes.
Water Jet
Laser Cut
CNC
Trying to figure out if we should just spot the centers and try the annular cutter on the drill press ourselves or just get the holes cut by the vendor.
We bought one of these many years ago and it’s our go to for most of our 1/2 inch hex bearings. The bearings are 1.125 OD and the reamer makes the hole closer to 1.126. if that’s a gauge for tolerance we have used that size on aluminum and plastic both with good success.
You can’t obviously drill a hole with it, but you can drill the hole larger incrementally with a tree step bit up to 1.125 and then use the reamer to finish it. It’s currently out of stock, but I’m sure they were not the only seller of it. The reamer could be run in a hand drill so it removes the need for a mill
We’ve had good luck using a 28mm (1.102") carbide hole saw and then using a hand reamer to achieve a press fit to the exact bearing being used. If you’re having the machining done by someone else, give them a bearing to work from.
1678 always undersizes our bores and post reams our bearing holes. Even the CNC router and our new CNC mills. We might soon work up a CAM procedure for boring our bearing holes on said mills. But the easy option that will always work is make it a tiny bit small and use a reamer to make it perfect.
You are not going to get a consistent light fit from a typical FRC style router. Best to go slightly undersize and ream it. For thin wall <1/8" I use a step drill that I have dressed the cutting surface to give me the desired fit. Vex use to sale a 1.126 reamer that seems to be permanently out of stock
On the side of “costs as much as a step bit, less than a reamer, and can save your bacon”:
You can always use a bearing clamping block as well on 2x1 tubes (or 1x1 in some cases) if there is a bit of space. This can really help if you can’t remake a tube for some reason and the hole is screwed up (machining error, robot impact bending the bearing seat during comp, etc)
Vex has them disconnected/out of stock.
WCP has them (or at least distributes vex). I thought they had their own variant, but I couldn’t find them on a quick search.
TTB for the win:
(They also have bushing version which is pretty neat, meant for the rounded hex bushings they sell)
These offset plates also exist, good for robot retrofit if a shaft needs a little more support
TTB seems to do a pretty good job releasing items, limited options, but almost everything is useful.
Andymark has their own variant here (there is also a variant for 1x1 tube):
Something I learned about last season that we will continue to use is a product called Loctite Retaining compound. It’s meant to as a gap filler for holes that are slip fit in metal to metal applications.
This depends on the machine, but for the waterjet I use, I set press-fit bearing aluminum holes to 1.126" and normal-fit bearing holes to 1.127". Some materials, like titanium plating, I always keep a couple thousands larger because they don’t tend to “give way” as much when trying to press fit.
Generally if we need it to stay retained we like to use a little dab of retaining compound(green loctite 609 or 603). We tend to design things in ways that naturally will keep the bearing retained. If you actually want a true press fit we will actually machine it that way but going on size or a thou over and using green saves time and effort.
I started laser cutting FRC parts last year with the industrial lasers I have at work. Even If I spent several hours fine tuning the beam parameters and adjusting the CAM offsets. I still wouldn’t be able to get in spec bearing holes.
I’ve been debating machining some bearing journals that have #10-32 tapped hole pattern and a reamed 1.125" +/- .002 Hole. That we could just bolt onto or laser cut pieces.
For a 1.125" bearing, yes, that would be the correct size. Anything 1.124-1.122" should be good.
Edit: sorry for machining size that we intend to ream, we use 1.100"
You totally can do it, but then you are actively needing to deal with tool deflection, cutter wear, finish quality, and how rigidly your part is set up for everything you do in order for it to be repeatable.
