Achieving the Smoothest Possible Surface Pre-Sanding

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Achieving the Smoothest Possible Surface Pre-Sanding

Postby honestabram » Fri Aug 04, 2017 4:29 pm

Hello All,

I have been running my new Lathe attachment on a camaster for about a month now. I'm about to do a six foot long pocketing tool path on the middle portion of a maple column, and I'd like to save myself some sanding.

When using a pocket toolpath to bring to the final thickness, what sort of cut-direction and what sort of bit have you found gives the smoothest finish? I've experimented between rastering in the direction of rotation and also parallel to the Y with a half-inch End Mill. There seems to be a trade off. More chatter when cutting around the axis, and significantly decreased rounding resolution when cutting along the y axis. I think I'll try a 45 degree raster to nearly the full depth and see what sort of result that gives. What do you prefer?

Also, I've been using the half-inch end mill. I don't think it'd be worth it to switch to a ballnose. Has anybody attempted to use a spoilboard surfacing bit on the lathe? It seems like it might not go well, but I'm hoping I'm wrong and I can use my nice Amana surfacer to give it a smoooooooth finish.

Any feedback is appreciated.

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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby Leo » Fri Aug 04, 2017 4:53 pm

I am a bit confused.

You have a "lathe?" on your camaster?

Or do you mean you have a Rotary axis on your Camaster?

Lathe, is extremely uncommon - rotary axis is the most common.

There is also a lot of erroneous nomenclature with people calling a rotary axis, an indexer.
Indexer is also very uncommon.

Do you have any pictures of what you are doing?
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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby honestabram » Fri Aug 04, 2017 5:32 pm

My bad. It is a 4th axis. However, camaster refers to it as a recoil lathe. Anyways, I've got some pictures. I gave it a bit more thought, and I don't believe you can get a smooth finish with any bit that doesn't have cutters spanning the full diameter on the end. So perhaps a straight cut plunge bit?
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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby Leo » Fri Aug 04, 2017 8:41 pm

Do you have any way to show us what you are trying to do?

Samples of the pocketing or a Vectric file - please don't violate model copyrights
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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby 4DThinker » Fri Aug 04, 2017 11:02 pm

For best result I'd use a large ball nosed bit rather than an end mill, then set the step over to a small amount, say 5%. The raster parallel to the grain direction. It will take longer, but you should be happier with the finish quality.

Large end mills on a round surface tend to throw/tear the grain fibers as they cut down the grain. The ball end bit shouldn't do that, but will take smaller stepovers to leave a surface requiring minor sanding to smooth out.
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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby Rcnewcomb » Fri Aug 04, 2017 11:38 pm

Are you asking specifically about this octagonal design, or for a general purpose answer?

Personally I would use a different technique (off axis side cutting) for the octagonal design, but that would not work for most other designs on the recoil.
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Re: Achieving the Smoothest Possible Surface Pre-Sanding

Postby honestabram » Wed Aug 16, 2017 3:47 pm

Thanks for the replies, fellas.

I'm asking for just a general purpose. the octagonal design was merely a function of saving on materials. The application I'm speaking of would just be a flat pocket on the 4th axis, which would just be an unadorned cylinder. I've purchased a mortising/bottom smoothing up-cut. It looks like a wide straight cut with only a slight angle on the vertical cutters, and the bottom cutters meet in the middle. I'm going to try that with a slight offset on x then try a range of feeds/speeds, once it arrives in the mail. I've got a half-inch ballnose that I'll try if I can't get good results with that. I'm just making a big push to get away from 3d modeling type toolpaths whenever possible.

Best,
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