interference fit

[stuffedpike20]

I am planning to adapt some Marina Hubs and need to drill out and fill the original stud holes.
The holes to fill will be drilled to 18mm, how much bigger should the plugs be to make an interference fit?
I am hoping to make the plugs from black bar on my very worn out lathe.

Thanks, John.

[oliver90owner]

Here is a quote from one of the many references on the internet for a cold press fit.

Using a 25 mm diameter, a H7/p6 fit gives a min interference of 0.001 mm and a max interference of 0.035 mm.

You can work out the range for yours.

Personally, I would not not consider doing the job that way - removing more metal than necessary would worry me; getting the tolerances absolutely correct would likewise be a challenge - too loose or too tight is to easy to achieve!

What metal will be left to support the replacement studs? Do you intend ensuring both front and rear surfaces are flat?

Me? I would thread and plug the existing holes and drill new holes on the correct PCD. No stress on the hub casting.

[stuffedpike20]

Thanks Oliver.
I was going to copy the Grumpys method, but your way seems easier.
How would I ensure that the threaded plugs that fill the holes do not move around? I think the wheel studs would be half in the threaded plugs, and half in the hub metal. And would a fine thread be better than a coarse thread?
Thanks, John.

[philthehill]

I would recommend that the Grumpys method is employed. It is a well proven method of rearranging the PCD.

[stuffedpike20]

You have not seen my lathe Phil. It is from WW2, looks like it was bombed, and I am not very good on it!
Is black bar strong enough for the plugs? I bought it because it is soft and 'giving'.
The plugs will have a 3mm flange.

[philthehill]

My lathe is well used and 125 years old and I have learnt to use it all from books and hands on learning. No experience of lathes before that except for a turning exercise on a Myford Seven when I was at senior school. If I can do it anyone can do it.
I would use EN8 for the plugs. The head of the top hat washer is 1" so can be turned from 1" stock bar. See my photos of the Grumpys Marina hub conversion for further details.

[stuffedpike20]

Thanks.

[stuffedpike20]

I had a go today at turning a plug from bright bar.
After a lot of re-grinding of the often blunt turning tool, slipping drive belt, and a lot of heat (my lathe has no cooling suds ), I ended up with one plug of dubious quality.
I wish I had the means of posting a picture, but I do not.

I wonder if there is a way of combining Olivers and Grumpys methods?
I found oil sump plugs on ebay with a 18x1.5 thread. They are shouldered and have a hexagon on top. The Marina Hub could be tapped to take the plugs. The hexagons could be turned off, or ground off the plugs before screwing them in, tightening maybe with a hammer and chisel on the side of the flange.
Then the new stud holes could be drilled.

Could this be the best of both worlds? A flange so there is no chance of the plug pulling through. and no interference fit putting stress on the hub.

[philthehill]

I have given up on High Speed Steel cutting tools and now use index tip cutting tools - use till the cutting edge begins to go off and then replace the tip. Easy and cheap.
https://www.ebay.co.uk/itm/MACHINETEC-1 ... %3A2334524
I do not have a suds system on my lathe either but what I use is Clarke cutting oil from Machine Mart. A little goes a long way. Just brush it on as required.
https://www.machinemart.co.uk/p/cutting-fluid-1-litre/

Make sure that the turning speed is right. A slow speed does not give a good cut.

Anything less than EN8 is suspect. I would advise that you do not improvise in using a drain plug as you do not know what the material strength is.
If you thread the top hat into the Marina hub and then re-drill for a 4" PCD you will be drilling/tapping through the threads of the top hat insert therefore reducing the holding capacity of the top hat insert.
The thickness of the head of the top hat insert is approx 4mm.

[stuffedpike20]

Thanks Phil.
I will have another go tomorrow.