Home brew 104bcd spider

hellmansam

Likes Dirt
Making the flat bottomed holes for the granny ring stubs was a bit tricky. I ended up misusing a couple of router bits as end mills along with a spade bit for some touching up.
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hellmansam

Likes Dirt
The chainring mount holes I drilled didn’t quite line up once I had the spider fitted up to the crank so it was time to really fudge things
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Chewed the holes out to my scribed circles and then ran a 10mm drill bit through them, chainring lines up ok now.
Then drilled a shitload of holes for the jigsaw to cut through
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Snapped a drill bit about 3/4 through that step, getting a bit impatient after a hundred or so holes o_O
 

nzhumpy

Googlemeister who likes bikes and scandal
Not a lot of meat left on the internal after the countersinking but still loving this.
 

hellmansam

Likes Dirt
Not a lot of meat left on the internal after the countersinking but still loving this.
No, but there's enough to bear against the chainring bolts, plus I'm thinking of backfilling the holes with Devcon once I make sure chain line and trueness are all OK. One of the holes lined up with a recess on the other side (top left in pic above) so it's thinner than the others. I have another identical plate so if I end up doing MkII I'll change the orientation to suit, 45 degrees will miss it.
 
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hellmansam

Likes Dirt
Dont stress about using router bits on ali, they work fine just take it easy.
Yeah it went fine in the drill press around 300 rpm. I can't remember where I read you could use router bits on ali but it stuck with me for a long time.
When the countersunk holes were smaller they turned out pretty nice, smooth and shiny with no chatter marks but the 16mm bit enlarging the 13mm hole wasn't stable enough. Probably would have been better doing it from scratch with the 16mm bit, or with a Rotabroach bit
 

SummitFever

Likes Bikes and Dirt
I cut alu all the time using a tungsten tip wood saw blade. A tungsten tip blade will last a surprisingly long time cutting alu. You do need to hold the saw "back" as the alu wants to grab the teeth and give too high a feed rate.

Spider is looking good. One question though, did you say this was for a Shimano crankset? If so, how are you going to replace the existing spider or is the new one going to use the granny ring bolts to mount up and then you'll cut off the arms of the older spider?
 

hellmansam

Likes Dirt
A fun back yard Macgyver machining project, but Looks like it weighs a ton. Couldn't have used thinner material?

Earlysport
Weight is 125g with a little bit to go from final shaping. But I need to take some off the granny ring stubs for better alignment and keep the thickness at the bolt holes. Some McGyvering of a case trimmer length gauge could work for this and keep the faces of the stubs true.
 
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