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Help laying out a 4 spoke wheel.

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markknx

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#1
I am stepping out of my comfort zone and want to make a 4 spoke hand wheel. My worry is I am doing it wrong or the hard way. I plan on doing it on a rotary table. I know I have to off set the cut of the spoke off center by 1/2 the spoke. not real sure how to come up with the proper amout of angle to advance the table. Or if I should just mill the circle between the hub and the inside of the wheel then offset the cutter by 1/2 the spoke then advance it till it clears the hub drill the hole. advance thr cutter to the inside of the wheel drill that slot between the two repeat for all four spokes (X8) then center back on the hub and connect the slots.

Here is a sketch of what I want to do. Thanks for any help.
Mark

20150215_143221.jpg
 

mzayd3

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#2
My thinking is that the center of the quadrants for your spokes would not be the center of the bore, but where the edge of the two spokes intersect (just past the end of the arrow that reads 1" for the outside dimension of the hub). This would be the center of the rotary table, your diameter for the inside of the rim would be 2.750" adjusted with your x axis. The rotary table would be rotated 90*, your x and y axis would be used to create the sides of the spoke. This method would require 4 setups, but is easier to accomplish without the confusion of tool offsets and such. I hope my answer is clear.
 

markknx

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#3
My thinking is that the center of the quadrants for your spokes would not be the center of the bore, but where the edge of the two spokes intersect (just past the end of the arrow that reads 1" for the outside dimension of the hub). This would be the center of the rotary table, your diameter for the inside of the rim would be 2.750" adjusted with your x axis. The rotary table would be rotated 90*, your x and y axis would be used to create the sides of the spoke. This method would require 4 setups, but is easier to accomplish without the confusion of tool offsets and such. I hope my answer is clear.
mzayd, I agree. that point of intersection of the spokes is the starting point for the sides of the spokes.( the corner I sketch in by the 1" bore arrow) But if I am understanding you right you are saying center that point on the table (or make it the center of my radius.) this would change axis of the insideof the wheel if I am following you right. Moving theaxis point would cause the iner and outer circle to not be concentric. and it seems then 90 deg would over cut do to the cutter dia.
Am I missing something?
Mark
 

mzayd3

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#4
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*
 

Uglydog

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#6
I made an 8inch handwheel out of 6025 aluminum this past fall on my RT.
Also, out of my comfort zone.
I cut what I was able to on the lathe and then moved her to the RT.
Be sure you have a good way to dial in center.
I was surprised how much she started to move as I made chips.
Ended up resetting the entire piece twice.
As I learned to use the hold downs better.
I was also surprised by the amount of math involved.
The above recommendations are solid.
Don't forget to think in three dimensions.
What does the profile look like from the front and the back?
Think through the whole thing and each process before you begin.
This is doable!
I learned heaps!!

Daryl
MN
 

randyc

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#7
I think that mzayd3 uses the approach that I use for rotary table work - but correct me if I am wrong.

I make a CAD layout of the part (I use a free application from SourceForge called "LibreCad, which is similar to AutoCad - no connection with them BTW). After the drawing is complete, it's simple to define the tool paths required to produce the part, just as mzayd3 showed above.

Markknx, we feel your pain concerning this problem, LOL ! We CAN work out the tool paths without using a CAD program, after all, machinists did it for multiple decades. But why, unless you just want to practice your descriptive geometry skills :)

edited again, wish I could spell properly the FIRST time
 

markknx

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#8
Thanks guys, big help. the good news is thes pokes are going to be recessed in at least .25" so I can take a light cut with the numbers and if I miss just mill some out and start over.
Daryl, I made a center pin that fits MT2 in my RT so that not only help to line it up it also stops center drift so all I shoud have to fear is unwanted rotation. I plan to leave the center bore snug to the pin then bore to final size after. it is only a crank handle for my 4x6 bandsaw. However it is also a test of my skills (and nerves).
Thanks again guys I will post when I get it cut maybe this weak. If not it maybe a few months as I am waiting to hear when I can get my rotator cuff repaired.
Mark
 

RJSakowski

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#9
Here is the way that I would make the wheel.

Find the center of the rotary table with an edge finder or dial indicator mounted in the spindle. Set your x and y axis to zero at that point. If you do not have a DRO, you will have to account for any backlash in your lead screws. Mount your workpiece on the table so it centered on the rotary table. If you are going machine it all with the rotary table, the positioning is not as critical. I would put a sacrificial piece under the part so I could machine the entire thickness from one side.

You can machine your bore by offsetting the x axis by the 1/2 the diameter of the bore minus 1/2 the diameter of the end mill. Likewise for the inner edge of the rim. You can machine the outer edge of the rim and hub by adding instead of subtracting your end mill diameter. Use the crank on your table to rotate it the full 360 degrees.

To cut the spokes, offset the y by 1/2 the width of the spoke plus 1/2 the width of the 3end mill and cut to intersect the outer edge of the hub and the inner edge of the rim. You will have to do some math here if you don't have CAD. If you have CAD you can pull the dimensions from the drawing. Since your spokes are recessed, you can machine to just short of touching the hub and rim by sight and clean up. This will profile one spoke.

Now rotate the table 90 degrees and cut the second spoke. Use the same x and y dimensions as before. Repeat for the remaining two.

Now cut the arcs between the spokes by rotating the table. Again use some math or a CAD drawing to get the start and finish angles. When cutting the arcs, rotate the table to the start position with the tool path radius set on the x axis and the y axis set at zero. Rotate to the finish position to cut.

You will have to finish the recess on the reverse side by flipping the part and centering on the rotary table. Or you could mount it on a lathe and finish it that way.

Here is a drawing of your part with dimensions Just remember that straight cuts are made with the x feed and curves are made with the rotary table feed. The 15.83 angle is 15 49' 36" and the 36.87 angle is 36 52' 12" Spoked Wheel.JPG
 

Uglydog

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#10
IMG_1631.JPG IMG_1630.JPG IMG_1637.JPG I don't pretend to know if this is best practice.
I turned both sides prior to milling on the RT.
Center the RT, then center the work on the RT.
I ended up finding an 8inch piece of pipe. Faced both ends. Then clamped the work to the pipe.
Then she didn't move anymore. Perhaps it was the aluminum, as I was taking light cuts.
Then I centered her back in my 4jaw lathe chuck.
IMG_1631.JPG IMG_1630.JPG
 

markknx

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#11
Daryl I don't pretend to be anything more than a metal worker. Yeah I do have a pretty good handle on set up and basic use of the RT. I was just not sure on the layout for the spokes. not thanks to you guys I'm pretty sure I have it. I am using a sacifical piece of HDPE. It will be center drilled and also drilled in 4 spots (where the voids will be) along with the blank for the wheel. They will in fact be stacked and drilled. then the blank will be tapped, the HDPE will be counterbored and open opened to a snug clear hole. Then into the 4 jaw where it will be indicated to the center hole, then turned to dia., faced and the center bored to fit my centering pin on mt RT. the with the backing still attached on to the RT. to cut the spokes. The wheel will have a separate hub to mount it to the saw do to way it has to be machined to fit the saw. So I will not be able to get the deep spokes like yours.
Mark
 

markknx

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#12
Here is the little I got done today. I cut a blank from a 4x4 block. Also a piece of HDPE for a sacrificial backing plate.
20150216_111407.jpg
Drilled a center hole and 4 mounting holes in the part and the backing plate. Also tap the mounting holes in the part and counter bored the holes in the backing plate.
20150216_143016.jpg
Got it mounted in the lathe, and started turning. 20150216_221052.jpg
 

mzayd3

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#13
I just laid it out in cad. You probably know this by now, but each quadrant, allowing for 1/4" tool diameter is 58.35* of rotation on the rotab.
 

markknx

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#14
Hey guys,
sorry it took so long to get back to you guys, but time has been tight and this took a little more time than I thought it would
20150218_193716.jpg
Machining the Spokes using the rotab. This was very time consuming.
20150220_162243.jpg
Back in the lathe to profile the back and bore the center to final size .625

20150220_232829.jpg
Finished hand Wheel.
Next is to make the spindle adapter. The saw's vice lead screw has 1.125 sticking out but 0.75 is milled flat on 2 sides to hold the floppy handle. (not sure the proper name for these type of handles) You know the type that is slotted so you have to flip/fold it from side to side. So since I don't want the new wheel hanging on a 0.5 piece of shaft, I am going to bore the adapter 0.75 deep and then slot along its axis picking up where the bore ends. sort of like a spindle bore with a MT tapper, you know the slot where you drive the wedge. the adapter will be 0.75 in dia. but will be reduced to form sholder. the wheel will be a light press fit and then fuse welded with TIG to the adapter. the adapter will also have a set screw to hold it to the screw.
Oh and of course I need to make a cranck handle.

Mark
 

markknx

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#15
BTW anyone found a link to let the mods know how you feel about the new software? I'm liken it! little learning curve but seems a lot easier to navigate
Mark
 

Wreck™Wreck

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#16
Figure out the angular positions and walk off 8 radial slots, 4 at the small radius and 4 at the large radius, off set the RT 1/2 the spoke width + tool off set in 1 axis and mill 4 connecting slots at 90º increments. Offset the RT the full spoke width + tool off set in the same axis in the opposite direction and mill 4 more connecting slots. Keep in mind that when milling an inside shape where the center drops out the tool will have a tendency to jam the drop against part when it comes loose.

In this drawing I used a 1/4" diameter tool, changing tool diameter will change the part radii and the spoke width accordingly. Since you are probably not making this to someone elses dimensions I would rough it with a 1/4" tool and finish with a 5/16" tool.
The angular dimensions are rounded off to whole minutes so they may be a bit off at the end, wasn't aiming for accuracy just giving you an idea of a way to do it. You can do the math yourself if more accuracy is required (-:
Good luck

ra20ib.jpg
 

markknx

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#17
Hey,
Thanks again for all the ideas and help. Even though I changed my design it was all still helpful in gaining a better understanding.
Here is how in the end I decided to to do it. when I turned the ppart in the lathe adn faced the taper in the stokes, I also faced two rims. One at the outer dia. and one at the inner dia. these set refference points for the spoke lenghs. then I moved to the mill centered the rotab in the mill and then the part on the table. Next I moved the X axis left 0.2 and set Rotab at 348deg (12deg. off cen.). Next I touched off the two rims recorded these numbers adjusted to allow 0.020 for clean up. This gave me my start and stop points for the spokes. I cut each side of the spokes by moving X right or left 0.2 and advancing the rotab to the spoke angle.
Once all 4 spokes were rought out and I zeroed both axises. it was simply a matter of picking up the ends of the slots for the spokes, and turning the radius cuts. On the first space I just cut the 4 slots. this left the center in the way while doing the clean up. so live and learn, on the next 3 I milled the hole space out. This worked so much better. I then just repeated this all over again just this time using the final dimentions.
I do have to learn how to draw with a cad program. any body got a good web site for this. I have libreCad on my computer But still have not got it figured out.
Any way thanks again guys. And Daryl nice work on your handle.
Mark
 

markknx

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#18
So I finally got the time to finish the crank wheel for the saw. Here are some photos.
20150222_192600.jpg
The adapter for the end of the screw finished and ready to be welded onto the wheel. Note the slot at the bottom of the adapter, it is cut into the bore. this is because the end of the screw shaft is milled to a flat on two sides.
20150223_141628.jpg
20150223_141500.jpg
The Crank wheel installed on the saw.
20150222_191057.jpg
The original Floppy crank. You can see here what I mean about the double flats on the end of the shaft. And why it was well past time for it to go.
Now with one good spin of the wheel I can move the vise jaw a good inch. I know it may seem like putting lipstick on a pig, but this little saw has cut anything I have been able to fit into it.
Thanks again to all those that chimed in to help.
Mark 20150222_192332.jpg
 

hman

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#19
FYI - Swarfrat Enterprises has a 2 volume DVD entitled "Mini Machines 202: The Rotary Table" It's available from Little Machine Shop, their part number 3406. It does a pretty thorough job of covering how to use the rotary table - setup/centering, reading the degree vernier, use of dividing plates, etc. etc. Among the topics covered is a detailed description of how to make just such a 4-spoke wheel.

Cost from LMS is $40, and well worth it IMHO.
 

markknx

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#20
Thanks John, I'll add that to my tools to buy. Hey wait thats one of those things the wife could get for my birthday. and she still has time. My next project is to built that part you have as your picture.
Mark
 
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