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Old 06-19-2005, 01:05 PM   #121
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Default Smooth comms

At the Reedy Race in May, I saw a engine builder (believed to be from Japan) with previously cut comms that were unbelievably smooth...I could easily see my reflection in them. Does anyone know how to achieve such results??? Didn't recognize his lathe as one of the typical brands.
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Old 06-19-2005, 01:15 PM   #122
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Quote:
Originally Posted by JRX-S Bill
I have only seen what you describe when a lathe motor has been connected backwards. Check to make sure that your lathe motor is running in the correct direction.

The armature should be rotating away from you as you look downward at it. Which is clockwise when looking at the armature from the comm end.

Bill
I have checked, and triple checked what youre saying, and it is indeed spinning away from me. I believe i have solved my problem though.
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Old 06-19-2005, 01:19 PM   #123
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I have checked, and triple checked what youre saying, and it is indeed spinning away from me. I believe i have solved my problem though.
Great!
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Old 06-19-2005, 01:25 PM   #124
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Boomer-
You've said that you like your cobra lathe. I've had one for almost a year now and the quality of the cut has been diminishing, even with new bits. Are you shimming the arm on both ends to keep it from moving between the v-guides? Or are you using the two plastic shims on the end w/a pinion gear to keep it from moving as the manual suggests (at least I think it does... I've tried this and I get a better cut from just shimming both ends). Any advice on how you have yours set up? Thanks.
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Old 06-19-2005, 01:37 PM   #125
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I had the windings of one of my Monster armatures hit the left v-block on my Hudy lathe and nick the wire winding that are machine wound a tad higher than normal. Since then, I have my lathe blocks properly spaced so I can always include a pheonic (sp?) washer on the non-comm side to space that end of the armature away from the block.

Have seen multiple people have this exact same issue over the past couple years, so it's probably worth posting this for the benefit of all.
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Old 06-19-2005, 01:42 PM   #126
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Hope this makes sense. First I put on a washer (I have two of these they are very hard and very shiny.) then put the arm in the lathe. Then on the other side of the 'way' I put the other washer then a brass spacer that is about 1/8 in the thick then the lock ( a coller with set screw) I use a piece of paper to check the "play" between the outside washer and brass spacer. I have never had any trouble, and my arms always come out 'mirror finish' Then I use a pencil eraser on them to finish it off. I take the arm out and use my xacto knife to clean between the segments and run a ball point pen down the segment spaces to take off the rough edges.
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Old 06-19-2005, 01:52 PM   #127
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Quote:
Originally Posted by Trixter
Hope this makes sense. First I put on a washer (I have two of these they are very hard and very shiny.) then put the arm in the lathe. Then on the other side of the 'way' I put the other washer then a brass spacer that is about 1/8 in the thick then the lock ( a coller with set screw) I use a piece of paper to check the "play" between the outside washer and brass spacer. I have never had any trouble, and my arms always come out 'mirror finish' Then I use a pencil eraser on them to finish it off. I take the arm out and use my xacto knife to clean between the segments and run a ball point pen down the segment spaces to take off the rough edges.
So, is it actually the eraser that brings the comm to 'mirror finish' condition?

Bill
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Old 06-19-2005, 01:58 PM   #128
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No, actually ther eraser takes a little of the sheen off the commutator, but according to motor experts, that is what you want. It has worked out great for me over the years.
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Old 06-19-2005, 02:16 PM   #129
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Thanks.

Oh, I do the knife and ballpoint pen stuff while the armature is still in the lathe. Seems a bit easier while still fully supported.
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Old 06-19-2005, 02:19 PM   #130
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for that mirrow shine, try using a dollar bill
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Old 06-19-2005, 02:19 PM   #131
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or a piece of leather...
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Old 06-19-2005, 06:13 PM   #132
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dakrat,

If I use a $100 dollar bill, will I get a $100 shine?

Thanks for the tips.

Bill
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Old 06-19-2005, 07:49 PM   #133
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Quote:
Originally Posted by JRX-S Bill
dakrat,

If I use a $100 dollar bill, will I get a $100 shine?

Thanks for the tips.

Bill
maybe......
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Old 06-21-2005, 08:27 PM   #134
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Guys the right way for a comm to look when it comes off of a lathe is like the back of a cd. You should see different colors like the back of a cd. Just because you get a mirror finish after you cut doesnt mean your lathe is cutting right. When you finish breaking in your motors, to check for roundness use your pinion wrench and spin up the motor at 5 volts and put the wrench on the back of the brush where the shunt is. It should feel like the motor is off. Meaning little to no vibration. Also brush hoods go out of alignment all the time. The reason aligning both at the same time is bad is because you have compensate for brush cocking. I dont care what anyone says, you do losse 1-3 degrees of timing if you dont align the hoods.
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Old 06-24-2005, 05:05 PM   #135
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How much on average is taken off the comm during a cut? Lately I have been averaging .003".
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