16-11-2015 01:02

kitare102

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

Hey, just wanted to chime in and point out that if those 1.125" holes are supposed to be for bearings, you'd need to adjust your dimensions if you wanted them to fit properly. That tolerance is on the edge of being a press fit, though usually I see press fits being .001" under the bearing OD. For a slip fit you'll want larger, around 1.126", and a free fit even more. All depends on how you want the bearing to interact with the plate. Otherwise these are great revisions from the previous drawing.

16-11-2015 01:13

Cory

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

+0/-.0005 is our standard tolerance range for a bearing press fit.

16-11-2015 01:40

Chak

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

Wow... that's a lot of zeros. How do you guys hold that tolerance? (especially the +0)

16-11-2015 01:47

Cory

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

It's a total tolerance of .0005. the acceptable sizes range from 1.125 to 1.1245 for a R8 bearing press fit. +0 just meant no bigger than the nominal size of the bearing.

This is (relatively) easily done via circular interpolation on a quality closed loop CNC mill (this is what we do), or via reamer or boring head on a manual/CNC vertical mill in good condition/proper alignment.

16-11-2015 15:08

Chris Endres

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

The drawings look better than the first, hands down.

However, I'd like to suggest thickening the ribs (the 45 degree spokes) to .375" or maybe even .5". This is because you might see the two plates warping or bending as the fly wheel spins (if COM is off-center) or as the balls ride the curve. You'd especially want to thicken these if you plan on this being used as a demo robot for a few years, or a design used in and actual FRC game.

There are a few other spots where I'd recommend thickening, like the wheel bearing holes and the little material holding the top of the plate to the bottom (I'd post a pic of it circled, but I'm not able to atm).

Overall, looks good.

16-11-2015 15:52

Jared

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

The drawings look pretty good. There are so few real engineering drawings posted on CD.

I'd move the 2.184 and 8.625 dimensions for bearing pockets so that the dimensions aren't inside the part. Also, you should move the 18.604 dimension all the way to the bottom so it doesn't cross as many other dimensions. I would also modify your sheet format so you don't have all that extra unused stuff in the title block and maybe increase the scale a little bit.

It looks like you have a CIM motor mount on this plate. The R1.260 dimension is duplicated in both views. Also, the .160 diameter holes are too small for #10 bolts if you're mounting a CIM directly to the plate.

If I were doing the drawing, I'd use ordinate dimensions and use one of the bottom corners as a datum for the weirdly shaped pocket. It will make life easier for the guy who has to input all this geometry. You may also want to add in the angles as reference dimensions too.

Your center bearing appears to be missing a dimension - I can't figure out where it goes left to right. There's also tolerance stackup on the y location of the two bearing holes. In the worst case they will be off by .015".

For the bearing holes, I'd talk to whoever is making this part to see if they think they can hold +0/-.0005.
EDIT: How is this being made?

16-11-2015 20:46

asid61

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

Definitely better than the last one; much more readable and more intuitive.
Seriously, why do you want the pockets at all? It's not as if you have a strict weight limit here. If you really want to cut weight, then just make it out of 1/8" and don't pocket. This plate is still a nightmare to make on a manual machine. It would be perfect for a CNC, however.

Have you used baseline dimension before in Solidworks? It's very handy. Click on the drop-down arrow underneath "smart dimension" and select "baseline dimension". Then select one edge to dimension everything from, and click on everything you want to dimension to in quick succession. This will clean up your dimensions immediately and prevent them from crossing each other.
You also might want to change 3-decimal dimensions into 2-decimal wherever possible. For example, the 6.198 dimension is extremely hard to measure, so marking it to a lower precision would help. Same goes for the 18.604 dimension on the bottom; does it really need to be that precise?

You should write the material down at the bottom. Most likely 6061 T6, but it's good form to put it in.

16-11-2015 21:51

Monochron

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

We decided to pocket for two reasons. First, to act as windows into the shooting track so that we can better see what is going on. The whole purpose of this build is to learn as much as we can about shooters and having everything as open as possible helps with that. Second, to get practice in pocketing in case we need to use it during build season. Just having your guys critique the pocketing job went a long way towards us understanding it, so thanks

I hadn't heard of it until it was mentioned here but, yes, it looks like it would be perfect for this piece.
The 6.198 in particular defines where the CIM pulley mounts in relation to the Wheel pulley. I was going for a c-c belt run so I thought that high precision would be needed.
Doh! Thanks. We had discussed that we were going to use whatever the shop had on hand (6061 in this case) but it is better practice to type that specifically.

16-11-2015 23:16

asid61

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

I would show this to the sponsor and have them give you feedback personally. That would probably be the easiest way to ensure that it's easy for them and you.
If you have a local community college, it would be a good step to see if any students can take machining courses there. Not only does it teach students about metalworking (and designing with machinability in mind), but the team also might get access to the machines there.

16-11-2015 23:51

Monochron

Re: pic: TerrorBytes 2015 Shooter Plate (Drawing) [Rev 2]

Yeah, sent them over with my concerns this morning. Hopefully we can figure out the best way to get this done. In retrospect I know they don't have a CNC on premises, but they may be able to recommend us to a place that does . . . we'll see.