Spokes Again...cad Help Please

[RVJimD]

I found the recent post on making a four spoke hand wheel. That helped a bunch but I think I need some help from one of you CAD types.

The drawing the Wreck made sense but I think since my dimensions are a bit different I need different starting and stoping angles?

My pulley wheels are 2.25 OD and have a 3/4" hub in the center. On my testing, it looks to me like a 1/4" end mill at .525" from center is about right for the start of the inner radial slot. And, I moved out to .800" and that looked good for the outside.

The thru hole is the test hole I did just to see what I didn't know about this! I really would like to do five or six spokes, but I am game to start with four.

Thanks,

Jim

 

[RVJimD]

I bit more info and questions...

Here is one of the posts from the thread I found on the site here referring to the task of making spokes...

yes, i see what you are saying. the inside radius of the rim would not be concentric with the outside radius. use the bore center as the arc center to maintain concentricity.

1) set the tool to cut starting outside the hub, but on one side of a spoke.
2)use the axis parallel to that spoke to advance to the inside of the rim.
3)rotate the table 70.9* towards the next spoke.
4)use the opposite axis to define the other side of the cutout (or one side of the next spoke).
5)rotate the table 70.9* the opposite direction.

this should complete one pass to complete a cutout.

i got the 70.9* from: (((circumference - total spoke width)/ circumference) * 360)/4

((3.14*3)-2)/3*3.14*360/4

This means that you will only be using 78.78% of the 360* for four spoke areas.
283.6* divided into four arcs is equal to 70.9*

I don't have a a problem trying to do my own math, in fact I would like to learn this part so I can make adjustments to suit my needs. In the quote above I don't see some of the variables, like

Inner and outer diameter of the void
Diameter of cutter
Spoke width
Number of spokes

Thanks for any help!

Jim

 

[mzayd3]

Well, there were some problems with my answer. I did not initially take into account cutter diameter. The final degree of rotation was, if I recall, 20* less than what I said here. However, the diameter is referenced as the circumference. The spoke width is used in the total spoke width. The inner and outer diameter is actually the difference in travel on the x and y axis.

If you know the minor diameter, that would be helpful as well as the spoke width. I'd be happy to try to walk you through it. But, just like me, you shouldn't take my advice too seriously!



Sent from my iPhone using Tapatalk

 

[RVJimD]

Be happy for the help, and I won't blame anyone but myself if it doesn't work out the first time!

Here is a sketch. Overall OD is 2.25" spoke width of .25" five or six spokes, there is a delrin hub in the center that is .75" OD, then I want to leave a 1/8" inner rim, then the spokes and voids, and a 1/8" outer rim.

Remember, I would be fine learning how to calculate this if there is a formula for that? Once i make a prototype, i may want to change the specs to make it look better. It would be much easier for me to do a simple bolt circle for simple lightening holes, but I wanted to try spokes.

I have the MH on my iPad but searching thru that I didn't find anything about spokes except for the strength analysis stuff related to castings.

Thanks for looking!

Jim

 

[Wreck™Wreck]

The drawing the Wreck made sense but I think since my dimensions are a bit different I need different starting and stoping angles?
View attachment 99235

Yes, if the relationship between the diameters change the angles change.
Download DraftSight's free edition this is what I use for simple 2D work like this, it's easy and
FREE

If you have any questions send me a PM

Same ID but different OD's result in different angles at the OD.

 

[RJSakowski]

I found the recent post on making a four spoke hand wheel. That helped a bunch but I think I need some help from one of you CAD types.

The drawing the Wreck made sense but I think since my dimensions are a bit different I need different starting and stoping angles?

My pulley wheels are 2.25 OD and have a 3/4" hub in the center. On my testing, it looks to me like a 1/4" end mill at .525" from center is about right for the start of the inner radial slot. And, I moved out to .800" and that looked good for the outside.

The thru hole is the test hole I did just to see what I didn't know about this! I really would like to do five or six spokes, but I am game to start with four.

Thanks,

Jim

Jim, on the thread you posted a few days ago, "Browser Based Apps/programs? Spokes?, I outlined a rather painless way to make spokes wheel with a rotary table equipped mill. That method works for any number of spokes. For the most part, it is not necessary to calculate any of the angles where your milling cutter starts and stops. This can all be handled with x and y offsets. You need to know what the separation angle for the spokes is, 120 for three, 90 for 4, 72 for 5, and 60 for 6. You also need your cutter diameter and spoke width and inner and outer diameter of your flange and hub. The model and drawing that I attached will work for any number of spokes. The only change is the angle between spokes which equals the table rotation you make to cut the next spoke.http://www.hobby-machinist.com/posts/290779/

 

[RVJimD]

Bob,

Thanks. I'm looking back at that thread now. I need a bit of time to study it...

Jim

 

[mzayd3]

So, the inside diameter of the spoke cavity is 1.000 and the outside diameter is 2.000?

So... (Here comes the math)

pi * r = circumference

Major diameter = pi * 1.000
= 3.14 inches

Five spokes @ .25 inches = 1.25

3.14-1.25 inches = 1.89 inches (circumference - total spoke width)

1.89" is the total useable arc length including the cutter diameter.

Divide that by the number of segments (5) to get .378" per arc length.

To further compensate for the tool (.250 end mill), the arc length is .128"

The end amount of rotation is a ratio of arc length per spoke/circumference*360

Your total is 14.66772 degrees.


Someone please double check my math- sorry entropic, I have had a few- but I am in a hotel, so I should be fine



Sent from my iPhone using Tapatalk

 

[RVJimD]

Mzayd3,

I think I will try to plug that into a spreadsheet tomorrow and then try it on the mill. My head hurts from looking at the numbers.

Thanks to everyone!

Jim

 

[RVJimD]

Okay,

I slept good, I'm sitting here with a cup of coffee and a spreadsheet app and one question so far.

In one line you write, major diameter = pi * 1. I think this should be minor diameter? We basically have to do the calculation once for the small arc and again for the large one correct? So one is called minor and the larger one is major?

Thanks for all the help guys!

Jim