My First Real Part

[ACHiPo]

Hi,
I purchased a turntable for playing vinyl records, and need to fabricate/duplicate a plate to mount my tonearm to the turntable plinth.

I need some suggestions on how best to machine Delrin to match the profile of the Al arm board I’m replacing. Specifically the best way to replicate the large radius. I have a Bridgeport 3/4 clone and a rotary table which is the only way I’ve come up to machine the 3/4” radius other than getting it close on the bandsaw and finishing with a belt sander. Are there other/better alternatives?
The “square” parts I’m comfortable with, it’s just that big radius.

Thanks in advance.

 

[FOMOGO]

I would think a band saw, and a file would probably be the quickest. Belt sander might melt it, but you could try it on a piece of scrap first. The rotary table would certainly work, but set up would likely take more time. What kind of turntable? Mike

 

[ACHiPo]

I would think a band saw, and a file would probably be the quickest. Belt sander might melt it, but you could try it on a piece of scrap first. The rotary table would certainly work, but set up would likely take more time. What kind of turntable? Mike

It’s a very special Technics SP10R broadcast turntable.

 

[benmychree]

Delrin does not saw cleanly nor does it sand nicely, milling is best.

 

[markba633csi]

I would rough it out with the bandsaw and then file to shape
Delrin is easy to work

 

[FOMOGO]

Very nice. I have an old PL 350 I bought new. It needs some work on the auto return. I have it sitting in the shop waiting for me to get roundtuit. Mike

Quote: It’s a very special Technics SP10R broadcast turntable.

 

[ACHiPo]

Delrin does not saw cleanly nor does it sand nicely, milling is best.

Thanks John. What do you think about the idea of rough bandsawing and filing to shape?

 

[ACHiPo]

Another idea I had overnight is to use painter’s tape on the Al pattern and Delrin, use superglue to affix the pattern to the roughed out Delrin, the use a router with a bearing following bit to trace the pattern into the Delrin. Seems like it could work? Will need to keep the router moving to avoid melting the Delrin.

thoughts?

 

[ACHiPo]

Another idea I had overnight is to use painter’s tape on the Al pattern and Delrin, use superglue to affix the pattern to the roughed out Delrin, the use a router with a bearing following bit to trace the pattern into the Delrin. Seems like it could work? Will need to keep the router moving to avoid melting the Delrin.

thoughts?

I'm convinced routing is a good way to go, especially since I already have a template and edge trimming router bit which I can chuck in the mill for lower RPMs. I even have a couple holes I can used to screw the aluminum to the Delrin.

I'd like to find a temporary adhesive/double-sticky tape to augment the two screws. Nothing seems to stick well temporarily to Delrin. Any suggestions?

 

[ACHiPo]

I found some double-sided carpet tape in a drawer. I tested the bond on Delrin and it stuck but not too well. Perfect. That combined with 3 wood screws should hold things together well enough to rout the shape.

My Delrin block is 2.5" thick and I need 1.25" final thickness, so I used my 14" wood bandsaw to "resaw" the Delrin into a 1 3/8" and 1 1/8" thick slabs. Unfortunately my bandsaw wandered more than expected, so I used my jointer to bring the slab flat again, but lost most of my 1/8" buffer.

I used blue painter's tape on the aluminum template and used the carpet tape to stick it to the Delrin, then used wood screws into pre-drilled holes.


I ran two layers of blue painter's tape around the aluminum template to give me about 0.020" to go from roughing to finishing. I did knock the corners off with a handsaw before routing.

The routed finish turned out pretty decent--the biggest issues I had was user error, namely starting the router before placing it on the work, so I have a couple divots that I flattened with a file. Delrin definitely machines and files nicely. It also makes a BUNCH of swarf that sticks to everything even though I had a vacuum connected to my router.

Here it is in the plinth. I still need to drill and tap the holes to mount the tone arm and drill and countersink for the two SHCSs that hold it to the plinth.


I milled the dado/lip with a 2-flute HHS TiN mill. The bottom finish was nice, some scallops on the vertical wall, but it's good enough given that it will be against the plinth and not seen.