How much material does abrasives remove?

[Alberto-sp]

Hello. Sometimes, when I'm finishing a part, since I have a small cheap lathe I think in achieve the final dimensions using emery paper or similar but not sure about that.

So my question is, how much material can you remove using abrasive? Of course this is a tricky question. It depends in the abrasive and in the metal of the parte. But for Example let's say cast iron and sand paper 320 grit. Just to have a reference point.

I mean, putting a bar on the lathe and splitting the emery paper, how much could I reduce the diameter in a practical way applying 320 grit sand paper

Thank you

Best regards

 

[Eddyde]

Since there are so many variables involved, it would be impossible to give a precise answer. I suggest you do some tests; Take a couple turning passes off a piece of scrap, take an accurate measurement, use the abrasives to get the finish you desire then measure again. That should give you a good reference.

 

[WobblyHand]

Don't know the answer to the original question, but I do know about sanding a 19mm OD washer to the correct thickness. I was using 600 grit diamond on 1144 steel. Using a light touch, I would grind off about 0.0002" after about a minute or two of work. That was slow work, especially trying to maintain the overall thickness uniformly. I had a couple of thousandths of an inch to remove, so it took a while. Had to rotate the washer regularly so it wouldn't develop a tilt.

Obviously a coarser grit could remove more material faster, at the expense of surface finish. The thing about hand finishing like this is you have to think about maintaining uniformity of the surface you are working on. It's all too easy to round things that shouldn't be rounded, or introduce nonuniformities. I try to use machines as much as possible, before doing handwork. That seems to work for me.

 

[rwm]

One thing I have noticed is that if my machined surface is kind of rough to start, then the sanding takes off more material in the beginning and then slows down a lot. When you mic the rough surface you are really measuring the high spots and those are quickly removed by sanding. If I am going for a very precise OD (tenths) I usually lightly sand before using the mic. This also clears any stray chips.

 

[woodchucker]

too many variables.
grit wears down quickly. quality of the abrasive.
pressure, high pressure removes less, eats grit, burnishes more than remove.
are you moving the paper (resin) back and forth to keep the abrasive cool.
speed of the turning.

you can remove some good amount of metal, but it will be time consuming. I file to remove, and clean up. filing is faster at removing and smoothing, followed by sanding.

No way to answer, too many variables

 

[rabler]

As a rough rule of thumb on the lathe, personally if I'm trying to turn something to a close tolerance such as a bearing fit, I'll try to turn it to about 1 thou oversize and use abrasives from there. But it is really a balance between how accurate you can work on your machine, and how much time you're willing to spend with abrasives. So lots of trade offs between skill, time/patience, and ruined parts by trying to cut too close.

I certainly wouldn't start with 320 grit.

 

[Aaron_W]

Eventually, you can remove the entire part.

I will use a file or more often emery cloth to improve the finish, particularly with something like 1018 which tends not to machine to a nice finish.

If I need a very exact tolerance I will get close then use a file, or emery cloth to get to the final size. I stop to measure frequently as I go. I rarely use anything courser than 600 grit on metal, 1000 is kind of my go to with 1500, 2000 and 2500 used primarily only if I want a very polished surface finish. To me 320 is something I might use for woodworking.

 

[Alberto-sp]

Thanks for your answers. Now I have some knowledge about the topic