Reaming question

Hi,

I'm looking to fit a 4mm mild steel bar into another piece of steel, to the depth of 5mm or so.The hole doesn't have to be blind. I need it to be a press fit, so it stays on. My question is how do I get the hole to the right size? I'm considering drilling it to 3.9mm and then using a 4mm reamer to enlarge but will this be large enough and is it best to use a hand reamer or machine reamer?

With thanks,

Julian

A hand reamer has a tapered end so provided you have a through hole you should be able to adjust the fit by how far you pass the reamer into the hole. Have a prcatice on some scrap first.

J

Depends on the actual size of the mild steel bar.

If it is 4mm then a drilling of 3.8/3.9 mm will give you a press fit without reaming. but check what size your drills are actually producing - most drill slightly oversize.

We normally drill 3.8mm for a 4mm reamer to H7 clearance on 4mm ground mild steel.

Yes, check diameter of the bar first, also Loctite will get you out of trouble if it all goes wrong.

Tony

I normally drill 3.9 mm and use a 3.98 reamer, not many people will have such a reamer but 0.02 interference fit is enough. If you are still unsure then Loctite is your friend.

Clive

If your bar is supplied slightly under then a H7 fit would give you a clearance fit so as Jason says use the taper part of the reamer to get the press fit you want. Try it on a test piece first.

Ideally you would use a H7 fit hole and then use a bar slightly oversize i.e for a light press fit a p6 fit would be +0.012/+0.020.

An undersize hole of 3.8/3.9mm would be quite a heavy press fit for a bar of this size but it all depends on what size your bar is.

Thanks for your responses everyone, when the bar arrives I shall measure it exactly. I had to look up the H7 reference, I take it the H's refer to the the fit, lower numbers being tighter. Where do the P's come in though?

Julian

Capital H refers to hole tollerances

Lowercase h refers to shaft tollerances

Number 6, 7, 8 etc referes to the actual range of that tollerance

Thank you.

I found that a newish H7 reamer cut a bit oversize, a commercial 4mm dowel which measures 4.010mm was actually loose in the reamed hole (machine reamer). A friend of mine who is a toolmaker was not surprised and said they would put a reamer in a drilling machine and run in reverse and lightly stone it to get a firm push fit, sounds crude but they didnt pay for the reamers and the stores only keep H7.

Mike

The H7 reamer is supposed to cut 4.000m to 4.012mm - a push fit, not an interference fit.

Either use Jason's cut on the tape tip, or use a number 37 drill.

I suggest experimenting on some scrap first.

Neil

Yes, depending on the size of the bar the machine reamer might be too large then, a hand reamer might be a better bet. Number 37 drill?

Julian, may I recommend purchasing a set of Zeus tables **LINK**

You'll never regret it.

Yes. I was looking at those, I just wasn't sure that metric clearance tables were in them - obviously they are! I think I might invest in one thanks, Lofty

3.658 = No27

Edited By Lofty76 on 24/04/2015 21:43:36

Here is a tip that some of you out there may not know. Given the drilled hole sizes are the same, and all the machine settings are the same, a reamer will cut bigger if you use cutting oil (rocol etc.) as opposed to water based emulsion type coolants. This is a small amount but is sometimes useful. (I'm still toolmaking!) Roy M

If I can get the work in the fridge I get to a very close fit ,cool one and heat the other and this has worked for me.

Frank

.

Roy,

That's very interesting !

I don't doubt you for one moment; but I would be interested to understand how/why it works like that.

MichaelG.

Any reason you can't turn-down the end of the shaft to fit the hole, instead ?