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Turning brass
- Thread starter AlexM
- Start date
- Joined
- Jun 20, 2022
- Messages
- 234
You are probably getting deflection. The unsupported end is moving away from the tool and making it bigger (leverage basically). Put a center in the end of the part and use the tailstock would be a start. But you might get away with just using a couple spring passes.
Too much stickout on the tool too. And make sure it's sharp or you get more deflection.
Too much stickout on the tool too. And make sure it's sharp or you get more deflection.
Thanks, I'm sure that is it.
- Joined
- Apr 30, 2015
- Messages
- 11,888
You're getting kind of a ripply finish there- the workpiece stickout looks OK- I'm thinking something going on
with the cutting tool (maybe not sharp enough) or your carriage is loose somewhere- or your leadscrew/feed gearing is sticking.
Brass is a "tenacious" metal which means it initially resists cutting then suddenly it gives in and grabs and tries to pull the cutting tool in.
Usually it's best to not have too much rake on your cutting tool, and tighten up all the slides on your machine wherever possible except the
one you are currently using.
with the cutting tool (maybe not sharp enough) or your carriage is loose somewhere- or your leadscrew/feed gearing is sticking.
Brass is a "tenacious" metal which means it initially resists cutting then suddenly it gives in and grabs and tries to pull the cutting tool in.
Usually it's best to not have too much rake on your cutting tool, and tighten up all the slides on your machine wherever possible except the
one you are currently using.
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Your tool has an enormous tool nose radius. For a not so rigid lathe or a not so ridged setup, you need a small tool nose radius to keep the cutting forces low. I grind my HSS tool nose radius to 0.2 to 0.4 mm. That is so small, you can barely see it. At a slow feedrate (0.05 mm/min) and shallow cutting depth (0.05 mm) these HSS tools give a pretty good finish.
Turning a "long" bar using the lead screw, makes it easier to get a good finish and better diameter control.
Turning a "long" bar using the lead screw, makes it easier to get a good finish and better diameter control.
- Joined
- Nov 25, 2015
- Messages
- 9,335
one more thing. You have a lot of stickout on the tool from the tool holder.
it will also deflect, then snap back. You only need enough stick out to cut. Save the long stickout for reaching into deep cuts.
it will also deflect, then snap back. You only need enough stick out to cut. Save the long stickout for reaching into deep cuts.
And slide the toolholder into the toolpost further. Rigidity, rigidity...esp on a small machine get all ya can...
- Joined
- Jul 28, 2017
- Messages
- 2,522
If your cross slide has a lot of backlash, that will exacerbate your problem. Brass can self-feed with a positive-rake tool so it will act to pull the cross slide toward it, leading to excess material removal. +1 on suggestions for shortening the cutter length, reducing nose radius.
A standard nut and feedscrew have to have some mutual clearance so they don't exhibit excess friction. When moving the cross slide toward the work, the feedscrew threads push against the nut, reducing the clearance on the work-side to zero -- leaving a gap on the other side. When cutting materials like steel, the cutting forces push back against the carriage, but the zero clearance ensures accurate cutting -- the screw and nut act as a solid hunk of metal. If a material like brass "grabs" the cutter, the cutting force reverses, pulling the carriage forward -- and it can, because the threads on the opposite side have all the clearance. To test this, move your cross slide forward using the crank. Then push the carriage toward the work. If the backlash is large enough, you can feel the carriage move forward. If the backlash is fairly small, it might take a test indicator to reveal it -- but it WILL be there. Climb milling on a manual mill can exhibit self-feed related problems for the same reason.
A standard nut and feedscrew have to have some mutual clearance so they don't exhibit excess friction. When moving the cross slide toward the work, the feedscrew threads push against the nut, reducing the clearance on the work-side to zero -- leaving a gap on the other side. When cutting materials like steel, the cutting forces push back against the carriage, but the zero clearance ensures accurate cutting -- the screw and nut act as a solid hunk of metal. If a material like brass "grabs" the cutter, the cutting force reverses, pulling the carriage forward -- and it can, because the threads on the opposite side have all the clearance. To test this, move your cross slide forward using the crank. Then push the carriage toward the work. If the backlash is large enough, you can feel the carriage move forward. If the backlash is fairly small, it might take a test indicator to reveal it -- but it WILL be there. Climb milling on a manual mill can exhibit self-feed related problems for the same reason.