Hole size for given rod

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Hello Everyone -

I have look at topics on general tolerances, etc to find out what size to make holes to fit a rod of a certain size. Most of these are for smaller holes.

In general if you want a snug fit, with little to no play how much larger should a hole be that a rod is going to be fit into VS. the OD of the rod?

As an example, I have a 19mm rod that I am going to fit into a hole. is 19.12MM going to be a snug fit? Are there any resources that any of you use for this kind of thing?

Thanks!

Bill

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Are you asking about 3D printing? If so, you should mention this and ask in the 3D printing category.

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could be 3d printing for prototyping but I am talking in general.

There are different defined classes of fit, but I don’t see them to this size. I will likely 3d print a prototype(s) but then use the model for manufacturing with either CNC or some other method.

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This seems like a question for a mechanical engineer rather than a SketchUp question.

5

likely -

that is why I put it in corner bar, in case anyone with this experience was in here.

Thanks,

Bill

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You might try envisioning a piece of tissue paper wrapped around the end of the rod. That would add about 0.06mm per side. You also need to consider the material and how you are making both the rod and the hole. If you are drilling the hole and reaming it to size and turning the rod to close tolerance on a lathe (or using precision ground dowel pins), then the hole should only be about 19.05mm in diameter. If you are 3D printing it, then you are stuck with the tolerance and resolution of the printer and the medium. Unfortunately, if the latter, the actual final dimension also depends on the orientation and relative placement within the printer work volume. I’ve tried various pin-to-hole sizes in sintered-nylon and sometimes get a press fit and sometimes a loose fit within the same part using the same sizes for the holes and pins.

Either go fat and sand to fit or go loose and use epoxy :wink:

8

Great advice, the piece with hole in production is going to be CnC’d
aluminum and thebrodnfitting in will be carbon fiber rods.

Thanks Jim for a great right and the comparison to tissue paper!

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For 3 d printing the material you use and the type of fit will determine the allowance you have to include in your model. I have seen on the Shapeway site testing results of folks looking at same issue for a snap fit. My Guess is the state of art for 3d print will have sparse data base.
For actual CNC the values you allow can be different because of different material you probably use. ANSI has tables that include eight class of fits from class 1 loose to class 8 heavy force fit and shrink fit going from 3/16 to 7=> 8" hole My drafting room manual only has English units you need to find one with metric. I am sure you can find that on the web.

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Mac - thank you very much for your thoughtful reply! I think I have basics figured out for now. I really appreciate you giving me a bit of direction there.

Best,

Bill Nichols

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Maybe not a question for a mechanical engineer, but rather for a fabricator or tradesman.

When you spec a hole of a certain size, for a particular fit, you need to know what’s making the hole and what’s fitting into it.

I work in wood, which is looser than metal. Cheap drill bits, or even expensive ones made for wood, can be .020" off size. Let the bit get dull and it will cut a different size hole, depending on the type of bit: a spade bit will more likely rattle a larger hole, while a twist drill will compress fibers instead of cut and leave a smaller one. Drill a hole and measure to be sure.

Likewise, wooden dowels can not only be offsize to a surprising degree, and in either direction, but they can also warp to elliptical— in fact, that’s very common.

I have a large industrial mortiser and hand fit tenons. The difference between too loose and too tight is on the order of .005"

So you don’t think this is just the case for wood, try measuring name brand drills for metalwork and see what you come up with. I’m not sure the effect of sharpness on them.

I would guess that 3D printing depends on the exact formulation, perhaps even the brand, of your medium, the precision of the printer, the temperature of the print head, and the resolution you are working out. As these vary, expect the results to as well.

Check your carbon fiber for tolerance— what’s the manufacturer tell you?

After prototyping and in production, you will perhaps get different results. Talk to the fabricator when you are working up the final file.

For now, consider testing the process or printing small and reaming to fit.

BTW, metric or English, the amount of tolerance is the same. Just convert from one set of units to the other.

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Machinery Handbook is what you are looking for.

1 Like
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I was looking for the same info. It seems like the correct terms are allowance which defines the space to be left between the two parts and tolorance which represents the variation that occurs during manufacturing.

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Engineer’s Edge is a website with the info you are looking for

Other classes of fits are available also.