Press fitting

[funkychicken]

If I have a 3.14mm shaft that has to go into brass, would a 3.1mm hole give a good fit? I don't have any kind of presses so I can't make it to tight

[Tankstand]

Hi

A hole that is minus 40 micron puts it into heavy / press fit territory!

Check out this Limits of fit chart (http://www.wisetool.com/fit.htm)

You need to work out the kind of fit you want, then look at the hole or shaft chart and refer to the number under your hole or shaft size.
You will see a lot of plus or minus values, these are the number of microns required to achieve the desired fit.

So, a slight interferance fit needs the hole to be H7.....+0~+12 micron larger than the shaft. This is 3.14~3.152mm.
Very hard to achieve without micro adjustable boring heads.

It is always easier to make the shaft to size than the hole so the other thing to do is emery down the shaft to suit.

Hope this helps

Mark.

[Dave J]

Thanks for that chart also. I find it harder to find metric tables as there usually imperial.
Dave

[pipeclay]

For what you are trying to do a .oo15" interference is probably to much.

Rule of thumb is .001 to the inch.

Is it possable for you to be able to heat your Brass item(.Brass will expand very quickly).

You could do it with a Torch,Gas Cook Top or electric Cook Top.

If you wish to aid fitting also place your Shaft in the Frezzer for a few hours before fitting.

How much wall thickness is there in your Brass item.

Depending on the size of your piece of Brass and the amount of interference you may get a little distortion in the Brass.

If practical you would be better off fitting the Shaft to you Brass item and then finish machine.

If you heat the Brass set a pair of Inside Calipers to your finished OD of your shaft Plus .001"/.003",when the Calipers fall through your hole the Brass has swollen enough.

If its a through hole you will have to set up some type of Stop or Jig to locate the Shaft in the correct position.

If the Shaft has been in the Freezer it will not take long for the Brass to shrink,if not in the Freezer allow to cool by atmosphere or blow compressed air on it,DONT put it in water.

[bollie7]

If I have a 3.14mm shaft that has to go into brass, would a 3.1mm hole give a good fit? I don't have any kind of presses so I can't make it to tight
For that small a dia I'd be more inclined to drill (and ream, if you have one that small) the hole to 3 mm, then turn the shaft down to 3mm so its a nice neat sliding fit, then loctite it together. I'd think you would find the strength of the bond would be greater than the strength of the shaft.

How were you thinking of making the hole? I don't even know if you could get an expanding reamer that small.

bollie7

[funkychicken]

The item is question is this
http://www.woodworkforums.com/members/16720-funkychicken/albums/tools-timber/2394-bull-oak-awl.jpg

The brass inserts into the timber 20mm at 9mm dia, and stick out 12mm at 12mm diameter. Heating the brass is a no-no (technical term, most laymen won't understand) and I can't turn the shaft because it's hardened HSS. I could grind it but I can guarantee I'll stuff it up. If I drill a 3.175 (1/8") hole what would be the best stuff to "glue" the steel in with?

[Woodlee]

Grind a couple of shallow annular grooves around the shaft and apply some epoxy glue (24hr Araldite will do) into the hole and push the shaft into the handle ,once it cures you will have to split the handle to get it out .

Kev.

[pipeclay]

Can you fit the HSS pin to your brass before you put it in your bit of wood.

Can you drill a through hole through the bit of Brass.

Is the end of the HSS flat.

Brass is only soft .

If you can place the HSS piece into the Brass bit first get another piece of Brass and place on the end of the HSS and hit it with a hammer untill it is in the right position in your bit of Brass.

Dont you have a lathe.

Do you have an Engineering bench vice.

Use the vice as a Press and make up a suitable tool for pushing the HSS piece in.

That way you eleaviate the problem of hitting the HSS with the Brass packer and hammer.

[funkychicken]

Can you fit the HSS pin to your brass before you put it in your bit of wood. Yup

Can you drill a through hole through the bit of Brass. Yup

Is the end of the HSS flat. It's whatever shape I make it

Brass is only soft .

If you can place the HSS piece into the Brass bit first get another piece of Brass and place on the end of the HSS and hit it with a hammer untill it is in the right position in your bit of Brass.

Dont you have a lathe. I do

Do you have an Engineering bench vice. Yup

Use the vice as a Press and make up a suitable tool for pushing the HSS piece in.

That way you eleaviate the problem of hitting the HSS with the Brass packer and hammer.

I still need to know which size hole to drill

[pipeclay]

Just drill it at 3.1 as you first said.

Depending on the method you use to drill your Brass you may find the hole is oversize.

You could try drilling with a 3mm drill first and see how that goes.

If the 3.1 drill runs oversize and the 3mm dosent work you can allways grind the 3mm to cut oversize.

You may even have to use a Number or Fractional drill.

Just do a test or two in a few bits first to see what works best.

[bollie7]

what would be the best stuff to "glue" the steel in with?

Probably Loctite 660 or 620

www.loctite.com.au (http://www.loctite.com.au)

bollie7

[funkychicken]

I've tried with a 3mm bit, it's flipping impossible:doh: I drill in the lathe, but I don't trust either chuck to be accurate

[Dave J]

The cheap Chinese 115 piece drill sets would work good enough for this job. They have number, letter and fractional sizes in them. I bought a set a few years back, I think I paid $115 for them in a steel box, but have seen them in plastic cases for around $60.
There alright nothing to rave about but good for opening up holes to exact sizes.
Dave

[.RC.]

Make a d-bit and use it...

[pipeclay]

Probably wouldnt matter what he uses for the hole if his tooling is not up to it.

Even reaming the hole after drilling would be useless if his machines are useless.

one of the only possable allternatives with worn or shoddy machinery would be to make a small boreing bar,and bore the hole to .006" undersize, and finish with either a machine reamer or chucking reamer.

Hopefully you lathe is capable of boring a parallel hole.

The reamer will follow your hole but if your lathe is not capable of cutting true your buggered.

Dont attempt to drill and ream,your reamer will follow your crook hole.

Might be a job that needs to be subbied out or invest in higher quality machine tools.

[bollie7]

Funkychicken
You have to keep in mind what you are making, what its intended use is and then you only need the level of accuracy required for that application. Don't get carried away in over engineering the job. Remember if you are selling the tools you make, that time is money.
For your hole you could also try grinding a 3mm drill so it drills oversize. To do this grind the drill so that one of the cutting lips is longer than the other. basically putting the point of the drill off centre a little bit. You might have to experiment with the grind of the drill but I reckon you would go close to getting the hole size you require. You just need a sliding fit, then a few drops of loctite. the pin will not come loose.

regards
bollie7

[funkychicken]

My gear isn't to bad but it's not what you'd call precision. I've an AL-54b lathe.

Good advice Bollie, I'll just use a 1/8" bit and loctite