# Press Fit Hammer



## lellasone (May 3, 2017)

Hello, 

As part of my ongoing hammer project, I am experimenting with press-fitting the handle (2025 aluminum) into the hammer head (304 stainless steel). I currently have a 0.520" diameter hammer neck, and a 0.510 hole for it to fit into. However, I am somewhat at a loss to determine what the final dimensions should be. Ideally, I would like to have the two hold together just based on friction, but if need be, I could add glue as well.

In any case, I wanted to see what people thought about sizing the wholes and whether adhesive is necessary. 

Many thanks,
All the best,
Jake


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## mikey (May 3, 2017)

Jake, I am going to guess that a 0.010" press fit is ambitious. There are online calculators for this sort of thing but I would guess that a 0.005" fit might be more realistic. This assumes you have a suitable press. Of course, you can freeze the handle and heat up the head but you are likely going to have issues if you try for that 0.01" fit. 

Personally, I would try for a more reasonable fit - 0.002" and I would pin the head on and not rely on any adhesive. Nor would I simply rely on a press fit to hold the head on. With repeated strikes, the head will come loose at some point and may then become a missile. Just an opinion.


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## Tozguy (May 3, 2017)

If you are looking for the best friction fit then definitely heat the head and cool the handle to get the greatest temp difference possible. Be ready to assemble quickly as heat will transfer rapidly. Aluminum will deform relatively easily in an application like this so depending on how the hammer will be used consider the alternative of a slight taper and a maybe a screw on the end to lock the taper.


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## RJSakowski (May 3, 2017)

I would consider threading and Loctite but with only .020 left to play with, you will most likely require pressing.


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## Sandia (May 3, 2017)

I agree with the above posts, that the handle will eventually loosen up if not secured with some method. Don't thank Loctite will be the answer either. I would personally make the handle out of steel for this application.


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## kd4gij (May 3, 2017)

Aluminum into steal won't stay tight. I would go with a .001 press and pin it with a 1/8" dial pin.


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## wawoodman (May 3, 2017)

Agreed. Pin it.


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## EmilioG (May 3, 2017)

Is this a dead blow or a soft faced hammer? Any pics that you wouldn't mind sharing?


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## dulltool17 (May 3, 2017)

My take:

.0015 interference.
Heat Head; Chill Handle
0.060 roll pin thru


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## lellasone (May 4, 2017)

Mikey - What you are describe - the head flying off - is my worst nightmare for this project. When you say pin the head on, do you mean drilling a pin through the side of the head through the portion of the neck inside the head? 

Tozguy - Any chance you could expand on what kinds of use case would make one option or the other more appropriate? 

Sandia - That's a good suggestion. I wen't with aluminium for this handle because it was light (and free) but in the future maybe I will try using steel and then drilling it out to help with the weight. Would steel perform better as a press fit? 

Emilio - Neither, it's a regular steel hammer with a point on one side. My school has a competition to see how quickly a (terminally damaged and irreparable) piano can be reduced to pieces small enough to fit through a 6" hole. Current students are not allowed to use traditional hand tools (sledge hammers or the like), so I am bringing a few pieces of scrap metal that happen to have been arranged in a hammer like shape (which, just to clarify, is exactly what that rule is intended to encourage).

Dulltool17 - I have been having more trouble than I would like to admit figuring out what a roll pin is via google. Do you mean these kind of things: Harbor Freight Link.

Everyone - Thank you so much for responding, I have been consistently blown away with how welcoming and helpful the Hobby-Machinist community has been (even in the face of silly questions). 

At this point, it seems like there is a pretty strong consensus that pining it is the way to go. Does a 1/8th diameter brass rod seem like a reasonable option? My plan would be to sand the handle down a bit more till it will press fit in without LN2, and then insert the pin from the side through the hammer head. Not sure how to get the pins to be flush with the steel though, belt sander maybe? 

Pictures as requested:


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## mikey (May 4, 2017)

lellasone said:


> Mikey - What you are describe - the head flying off - is my worst nightmare for this project. When you say pin the head on, do you mean drilling a pin through the side of the head through the portion of the neck inside the head?



Yes, I would use either a roll pin or a solid pin (steel). Roll pins are hardened and are perfect for this job. If you drill a 1/8" hole through the side of the head, right through the part of the handle that fits inside the head, that roll pin will hold the head solidly. If it ever needs to come out you can drive it out with a punch. The roll pin can be ground to length so it fits the width of the head perfectly.


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## Tozguy (May 4, 2017)

Ah, a hammer for demolition needs to be pretty solid. A small hammer like that will have to work very hard to reduce a piano to 6'' pieces so pinning is a must. Does the 'scrap metal' need to be assembled into a hammer on site? If so maybe make it a close slip fit and use a couple of set screws into pockets instead of a pin to secure the head to the handle. That way the screws can be tightened on site as needed.

BTW you might have trouble passing that off as scraps, it sure looks like a beautiful hammer to me.


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## whitmore (May 4, 2017)

At only half an inch, a 1.5 mil interference fit is VERY agressive, heating
the iron to 400F only expands the hole by 0.0011.   I'd cut it down to .001 interference.
If retention is an issue, drill and bellmouth an exit aperture in the head, and peen
the handle to rivet it in place.   If it has to be pretty, bellmouth the head
and center-bore the handle, and force a cone into the center-bore
with some loctite or a light knurl, to wedge the assembly.

0.005" of bellmouth is a lot (wood-handle  hammers use twenty times that).


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## cascao (May 4, 2017)

Have seen many projects like these here before and it let me thinking about metal handles vs wood handles.
I think wood handle is more confortable due some vibration dampening but yes, metal handles look awesome and is durable.
Don't you guys who made metal handles had some harsh feeling?


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## Tony Wells (May 4, 2017)

Roll pins are not hardened. They are soft. Many people incorrectly interchange the terms "roll pin" and "spring pin". A roll pin is actually a strip of metal rolled into a size slightly larger than the hole it will fit, and compresses as it is pressed or driven in. Once removed, it will not return fully to the original size. It is malleable.

On the other hand, a spring pin, aka split pin by some, is hardened and is a single turn of spring steel that is just shy of the actual calculated circumference of the target hole, giving it the gap, or split. If measured, they are a bit oversize as well, like the roll pin, but unlike the roll pin, when removed they will return close to the original size. They are considered reusable, whereas true roll pins generally are not.


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## mikey (May 4, 2017)

Tony Wells said:


> Roll pins are not hardened. They are soft. Many people incorrectly interchange the terms "roll pin" and "spring pin". A roll pin is actually a strip of metal rolled into a size slightly larger than the hole it will fit, and compresses as it is pressed or driven in. Once removed, it will not return fully to the original size. It is malleable.
> 
> On the other hand, a spring pin, aka split pin by some, is hardened and is a single turn of spring steel that is just shy of the actual calculated circumference of the target hole, giving it the gap, or split. If measured, they are a bit oversize as well, like the roll pin, but unlike the roll pin, when removed they will return close to the original size. They are considered reusable, whereas true roll pins generally are not.



I stand corrected, Tony.


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## Rockytime (May 4, 2017)

Thanks Tony. I was not aware of the difference between a roll and split pin. At 78 I was sure I knew everything. At the rate I'm going I'll soon be as smart as a teen ager.


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## dulltool17 (May 4, 2017)

Dulltool17 - I have been having more trouble than I would like to admit figuring out what a roll pin is via google. Do you mean these kind of things: Harbor Freight Link.


Yep!= well actually that is a spring pin, but it is what I had in mind.  I think 1/6" is big enough and 1/8 might be too big.

Maybe 3/32" (.093)


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## Tony Wells (May 4, 2017)

Well, just for fun, let's add a little more confusion. There is also a "groove pin". Basically a dowel pin with a linear placed vee bottomed groove rolled or pressed into it. Usually just one. But because the method of grooving is a displacement method, the edges of the groove are upset and make the pin fit tightly in a precision hole. Usually these work best in a closely sized hole and are pressed or driven in. 
A variation is a pin with upset serrations a short distance from one end only, sort of a "head" if you will. The advantage of these is they don't tighten up in the hole until you reach the serrated area near the end. So you can actually hand assemble something to check for alignment and fit before driving the pin into final positions. You will see these in assemblies where there is a piece captive yet not immobilized between two close fitting holes either side of it. Think gun parts like a trigger or hammer. They have to be free to move, but the pin obviously has to be secure against movement. It's just alternative to having the moving part with a clearance hole allowing a regular dowel pin in it. You won't see too many roll or spring pins in applications such as those.


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## scwhite (May 4, 2017)

wawoodman said:


> Agreed. Pin it.


That is what I would do to
Pein it with a ball Pein hammer make your handle long 1/8 
.001 or .002 press fit then Pein that 1/8 good and tight


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## westsailpat (May 5, 2017)

Nice hammer Jake , here is another thought ... Drill a clearance hole for a screw through the hammer head and c'bore it ,   and thread the handle for the screw  . Get it welded up and file it down and polish .


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## Chipper5783 (May 5, 2017)

This is a very good topic.  I encourage you to study up on "Limits and Fits" (see Machinery Handbook).  The general rule of thumb for holding reasonably well is 0.001" interference, per inch of diameter.  If you get enough interference, you absolutely can get it to hold without the cross pin.  We put 50,000HP though a 10" coupling (shaft size) with no keys, no splines - just a lot of interference (much attention to detail and specialty tooling).

Usually a person would bore the hole, measure it carefully and make to handle (pin) to the correct size for the fit you are looking for.  You are dealing with dimensions in 0.0001" and it is easier to hit that number on an OD than it is on an ID.

With aluminum and stainless, you can probably get 0.001"-0.0015" of interference together without too much difficulty.  Do you have access to liquid nitrogen?  You could certainly run a little test (or do a bit of number crunching) and figure out how much shrink you can get on the aluminum.  When you are doing a large shrink fit (and .0015 on a 1/2" pin is), make sure you are well set up and things go together fast (you get one chance and it last about 1 second).

Let us know how you make out, Regards, David


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## whitmore (May 5, 2017)

cascao said:


> ... thinking about metal handles vs wood handles.
> I think wood handle is more confortable due some vibration dampening but yes, metal handles look awesome and is durable.
> Don't you guys who made metal handles had some harsh feeling?



I've heard this from carpenters, that steel shank and even fiberglass are
hard on the tendons.   That little bit of shock that travels back up the handle
when a nail is struck... can add up.    Those carpenters preferred wooden handles,
and wanted the grain of the handle to be aligned so the growth rings were parallel
to the head-t0-claw direction.   

Makes sense to me (and my tennis elbow).    Comforting, that Dad's old wood-handle
hammer was like new for the first fifty years, and still functional at seventy
with the original handle.


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## Cadillac STS (May 6, 2017)

To make a piano fit through a 6 inch hole the main problem will be the iron sound board.  You need something with big mass to fracture the cast iron down to pieces small enough to fit through.  The small hammer is really nice but  you need something bigger.

My plan would be to burn the piano as it sits to ashes and put them through the hole.  Then all the smaller bits should be small enough to go.  That will leave the large cast iron sound board the wires are connected to and that would take something with mass to shock and break the cast metal like a sledge hammer or some metal in that form.


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## Cadillac STS (May 6, 2017)

Back to the press fit question and your specific hammer.  Could you drill all the way through the hammer head and press fit the handle all the way through but also thread the handle and have a nut on the handle on top of the hammer head to keep it from pulling through?


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## scwhite (May 6, 2017)

lellasone said:


> Mikey - What you are describe - the head flying off - is my worst nightmare for this project. When you say pin the head on, do you mean drilling a pin through the side of the head through the portion of the neck inside the head?
> 
> Tozguy - Any chance you could expand on what kinds of use case would make one option or the other more appropriate?
> 
> ...


What is this hammer used for


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