Drilling using MR-1

MR-1
1

Hello Group. I am needing to drill some holes for a 1/4-20 screw. The drill bit required is a #7 drill (.201)
What are your guys and gals using to drill number drills with. I dont think they make er20 collets for number drills…or do they.

Thanks,

Sam

2

.201" is just over 5mm, so you would use a 6mm collet. ER collets typically cover a 1mm range.

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Options for ya:

  1. helical bore with an end mill. Optionally pre-drill a pilot hole with a stub drill

  2. use a metric collet. A 6-5 mm collet should work

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4

7/32 ER20 collet is .219 and will close down to .201 just fine. You don’t need a metric collet (and a 6mm collet is .236, so you have to squeeze it more anyway).

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I use a 13/64 (.203) drill bit in a 7/32 collet for 1/4 -20 threads. I use a thread mill to create the threads with a pitch diameter of .05 , pitch diameter offset of .0512 and multiple passes (6 passes, so I don’t stress the small thread mill). This formula worked perfect for the 1/4- cap head screws I had on hand. I did try a regular 1/4-20 bolt and the threads were a little loose. In my model I use a hole diameter of .203. I’m using fusion 360. Hope this helps

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Awesome answers Yall. Thank you very much.

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What threadmill size did you use for this ?

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I use a Jacobs No 1A with a 1/2" arbor. You can find them on ebay fairly cheap.

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I use the Langmuir 1/4 inch single flute thread mill.

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What settings/steps did you use for this thread. We just setup our machine and did the exact same 1/4-20 with Single point thread mill and my threads didn’t turn out. I’m getting ready to try again and could use some help. I’m not used to single points.

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You have to tell Fusion how many teeth are on the thread mill.
Is your hole the correct size for a 1/4-20 thread?
Sorry I read your question wrong.

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Watch this video. Everything you need to know to get started.

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If you used the steps I outlined above and found the results unsuccessful, I think watching the NY CNC video titled “Thread milling :The Ultimate Guide WW187” on YouTube might be helpful. This video really helped me understand how to set up the thread milling in Fusion 360. I never model the threads in my model, I just model a hole. Also when I say “passes” I mean stepovers.

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