standard hole sizes

do you guys have any standard hole sizes/bolt sizes that your team uses for your bot? this year we are thinking of using as much 3/16 as possible because this is what our rivets are. Its a good medium in terms of strength and size. we will of course use other sizes when necessary. what do you guys think the cons of this system are?

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.196 - #10 / 3/16" clearance hole
.159 - #10 tapped hole
4mm - diameter of the smallest WCP endmill

Basically use these for everything. There’s a huge advantage to standardizing on a system and designing around it.

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I’m a big fan of the 3/16" hole pattern.

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You can follow this: http://www.engineershandbook.com/Tables/taphole.htm

0.201" (#7 drill bit) is the thru hole size for a #10 bolt, and as Andrew mentioned above a #10 or #11 drill bit will give you the proper size for a 3/16th rivet. A 3/16 drill bit will give you a hole that is just barely too small and annoying to work with. We use those two most commonly
0.201" is also the size to drill if you are tapping material for a 1/4-20 bolt which can be handy.

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My team (1836) probably made over a thousand .201/#7 holes over the course of the past season. It’s super convenient for use with 3/16 rivets, #10 bolts, and can easily be tapped for 1/4-20 bolts. .201 has been the magic number on our team for years and I don’t think we’re looking back anytime soon.

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The dual-usage of #7 seems handy, but most of the time the free fit for 10-32 bolts is annoying. I personally don’t like it at all, and strongly prefer using the close fitting #9 drill that Andrew indicated.

We .201 all the things.

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At this point the tradeoff is a looser fit on #10’s but a need to change tools or mess around for any tapping you may need to do. If you really want “standard hole sizes”, #7 makes life easy because you have an option for a free fit or tapped holes with #10 and 1/4-20 bolt sizes. At least for my team, using 1/4-20 hardware when we need taps take a lot less work/time than it would be to program new tools and work around different stuff in design/manufacturing, but it does have costs which need to be considered.

Only ever using one hole size for any baseline hardware (bolts, rivets, etc.) seems to be as standard as you can get…

Agree

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I dislike 0.201 (#7) because it feels too loose for #10s. If I’m milling or CNC’ing a part I can use the 0.196 (#9), and if I’m hand drilling it’s all match drilling anyway so 0.196 still works. Plus, rivets are supposed to be 0.193-0.196, so I like using #9 or #10 drill bits for everything. That being said, 1/4"-20 tap is a clean 0.201 as people have mentioned. It’s honestly a weird toss-up for me.
1072 is working on standardizing their hole patterns this year, and we’ll be paying close attention to this thread.

We are trying to have entirely 1/4-20 and 10-32 hardware this year sans a few specific items. I think it is a great idea to standardize your hardware as much as possible for many reasons:

  • Less searching for the right tools
  • Less searching for the right hardware
  • Less replacement parts to bring to competitions
  • Easier decisions to make during design

As for clearance holes, I’ve always gone straight to the charts, but there are some instances where its helpful for the clearances to be a bit tighter. If we have a full 1/32 bit set in the vicinity, I will often go a 16th or 32nd up (9/32" for 1/4") but the #7 bit is significantly tighter than the next 32nd up for a #10 hole. If I want a closer fit I go anywhere in between a #9 and a #7.

We never thought about standardizing hole sizes, but once we standardized fasteners, the number of different bits we regularly use went way down. For the robot chassis and frame, mostly 5/32" rivets and 10-32 machine screws.

Pre-drilled or pre-tapped holes in COTS components often suggest a different size; 3/16" rivets for the AM14U chassis when we rivet, 1/8" rivets for some spring hinges we got at Ace Hardware, #8 screws when securing versaframe in situations where the fastener is likely to be under extension.

And sometimes you just need something larger or smaller. This year we used 1/4" for the battery tie-down and securing the climber to the chassis.

With .196 you do get a closer fit for #10 bolts, but a looser fit for 3/16 rivets. I’m fine having a looser fit for bolts because things like locktite and locknuts let me sleep at night, but prefer a tighter fit on rivets where too much wobble can lead to even looser rivets. We use a #11 for rivets giving a .191 hole size (rando site to back that up).

Never had an issue with 3/16" rivets in .201 holes.

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.196 is my standard hole, because it’s a slightly better fit for 3/16 rivets (vs .201) and a tighter fit for #10 bolt clearance. If a looser fit is desired, it’s trivial to drill that out to .201 later, and 3/16 rivets will still work fine in these bigger holes.

I’m not a huge fan of the 5/32nd rivet / #8 clearance pattern used on Vex products, so I’ve typically designed these to be drilled out immediately for the bigger hole pattern. On 228, the team had a stock of a few thousand 5/32nd rivets to go through before we could standardize on 3/16, so we went with the .159 hole pattern on everything in 2017 and drilled out as needed.

The other nice thing about .196 - .201 is that you can tap it for 1/4-20 if you ever really need to and you can’t use a rivet nut. That said, there’s surprisingly little need for 1/4-20 hardware on FRC robots. Occasional bolts here and there, mainly for ThunderHex axles, but generally I prefer to use more smaller fasteners than to deviate from the #10 standard.

1712 uses a variety of COTS products for structural purposes, and that unfortunately leads to poor standardization of hole sizes.

In our early years, 1712 used 1" 80/20 extrusion for just about everything. 80/20 is designed for 1/4-20 hardware, so that was the early standard. That 1/4-20 has stuck as a default hardware size for a lot of the things we do (plus we still use 80/20 for some superstructure/manipulator/cross-beam purposes).

In the past couple years, we’ve moved a lot towards VersaFrame(particular for our drive base). That comes with 5/32" holes as the standard, so we initially used 5/32" rivets everywhere. However, we learned the hard way in Stronghold that 5/32" rivets aren’t always sufficient for FRC needs, so we stepped up many of the holes to 3/16".

So, in essence, we have a collection of different hole sizes and a lack of standardization. It can definitely cause headaches.

Wow, I feel like a minority here…
We tend to use a lot of #6 and #8 fasteners, which is great for availability cost and weight, but not as beefy in the strength dept. (Although still overkill in a most situations) however we tend to use 5/32 rivets and versa-frame patterns so…

We also tend to go totally overkill on the drive base. We have welded it for the better part of a decade so we are not reliant on the fasteners to take significant shock loading. For some applications (such as the 3/16 (or more) aluminum belly pans we often have used to lower center of mass) the methodology of attaching goes something like this:

When in doubt, double the count.
:rolleyes: Take of that what you will.