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| What was the thinking behind BA threads |
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| Will_D:
--- Quote from: Muzzerboy on August 10, 2019, 12:53:30 PM ---but most BA pitches are impossible to make on a lathe without a bucket of changewheels, --- End quote --- But why would you want to screw cut a 6 ba thread? You use dies! Dies when adjusted correctly cut a perfectly formed thread (including the roundy tops and bottoms) by a process of shear and plastic deformation. Screw cutting on a lathe really comes into it own when you haven't the physical grip on the work piece or the die to resist the torque. Just look at a pipe fitter cutting 2" x 11 tpi pipe threads - it certainly leaves its mark on the pipe from the pipe vice Or when you want to cut a unique thread like 40 mm by 1.5 or 1" by 50!! Simple screw cutting involves pushing a pointed tool (with no accurate tip radius) into the work, the crests of the thread are left raggy and are usually rounded of with afile! |
| djc:
--- Quote from: Will_D on August 10, 2019, 03:55:19 PM ---But why would you want to screw cut a 6 ba thread? You use dies! --- End quote --- OK, I will bite... 10 How was the 6BA die made? 20 With a 6BA tap. 30 How was the 6BA tap made? 40 With a 6BA die. 50 Goto 10 Screwcutting for BA could be made very logical if you approach it with the right mindset. Start with a 1mm pitch leadscrew. Gives you 0BA. Gear it 9/10 for 1BA. Gear it 9/10 x 9/10 for 2BA. You only need two sizes of change gear (and a very big banjo!). |
| timby:
--- Quote from: djc on August 11, 2019, 05:14:42 AM --- --- Quote from: Will_D on August 10, 2019, 03:55:19 PM ---But why would you want to screw cut a 6 ba thread? You use dies! --- End quote --- OK, I will bite... 10 How was the 6BA die made? 20 With a 6BA tap. 30 How was the 6BA tap made? 40 With a 6BA die. 50 Goto 10 --- End quote --- Not if you have one of these, |
| djc:
--- Quote from: timby on August 11, 2019, 06:44:56 AM ---Not if you have one of these --- End quote --- Looked a bit big for 6BA :-) And what, pray tell, do you think was moving the workhead when it was grinding the threads? A ballscrew, which is a fancy leadscrew, with electric cogs for pitch. So it was screwcut. You need to find an example that is not screwcutting. Maybe that lost episode of the A Team where they were locked in a barn and they filed a 6BA thread on a pitchfork handle. |
| DavidA:
One could say, tongue in cheek, that it was a far - sighted plot to make money out of model makers. 'I say, that man is using Metric screws on his British loco models. Fella should be horse whipped'. Dave. |
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