Dovetail keys

[JNewman]

I have recently had a problem with the sow block on my hammer moving. I have been making chisels that get welded on the end of a pipe. Imagine a wedge 3" wide 1 1/2 thick on the heavy end, tapering to a feather edge over 5" with a 1" shank on the heavy end. I am making these from 3" round 4340, so I am hitting pretty hard especially on the taper tool after I have the taper roughed out.
What is supprising is I would expect all that hard pounding using a taper tool on the bottom die would push the sow block back. However the sow block has moved forwards about 1/4-3/8" twice on me in the last few days. This is a real PITA to fix because I have to remove my treadle guard/tool tray and then beat on a punch to drive the key out. With the sow block moving forward (key drives in from the back) I would expect the key to have loosened up with the block moving, but it is really hard to get out, ten or so blows with a 12lb sledge before it STARTS to move.
After it moved the second time today I took a good look at the key. It looked like it was binding a little on the big end because of upsetting on the end. I ground that off and then fitted it with bluing, it could be a better fit but I think I am going to make a new longer key at some point so I can drive it in and out with no punch. I added an extra shim and now that its a better fit I greased it and drove it in. Hopefully this will fix my problem.
I have another dozen chisels to make next week so I will find out if it does.

[Nakedanvil - Grant Sarver]

Hey J! I'll tell you what I know and what I think I know. Nice to have a center pin, amazing some of the component forces involved. I like a center pin that looks sorta like a square head bolt or "T" bolt. I drill a hole in the middle of the anvil, nice if ya got a mag drill, but I've done it the hard way too. Then machine a slot across the dovetail of the sow block. On a hammer your size I'd probably use a 1-1/2" diameter hole and a 1-3/4" slot for the square head. The slot allows left-to-right adjustment. If things don't line up perfect front-to-back it's easy to make an offset pin. Long wedge is nice, use some of that 4340, forge it out and machine it. Grind both ends to a ball end to prevent mushrooming. Throw it in with a batch of heat treat, 40Rc is nice. Galling is caused when two material have nearly the same hardness (I just learned that a couple yeas ago). Glad to hear you're using lube on the key. Hope some of this helps.

[brianbrazealblacksmith]

There is a big difference in an Earth to Sun blow and an angled blow that doesn't have the whole Earth to back it.

[JNewman]

I hadn't thought of a pin even though there is a slot for one in the back of the bottom die. I can borrow a mag drill from my next door neighbor but I will have to send the sow block out for the machining, I think it is too tall and possibly too heavy for my little Excello Mill.
I wasn't using lube on the bottom key before, because the when I first used the hammer I did lube the key and it came loose a couple of times. But the new top key that I made and blued in works great with grease on it. Now that the sow block key fits better I figured it would be fine and will hopefully help with removal.

[nonjic]

Hey John, Pretty well what nakedanvil has said! nice to hear the hammers getting some work :)

[JNewman]

Part of what I was trying to get along in my first post is a thing that looks so crude, driving a wedge in to hold down the die only works properly when it is fit very accurately.

[ptree]

JNewman, Think wedge like a morse taper or Brown and Sharpe mill taper. Great finish, great accuracy, to get them to hold. If you see a little galling, I would reccomend Dow Corning MolyKote GN assembly paste, applied in a thin film. The stuff is dirty to work with as a little dot will spread to cover an entire arm, but is the best anti-galling at reasonable temp's of any lube-antisiezes I tested, and at the valve shop I tested all on the market I could then obtain.
It can be had in a toothpaste tube type container, and is also a great run in lube for before the auto-lube starts.

[forgemaster]

We have found with tapered keys that, they must bear all the way along the key, so yeh using blue is good, you need to drive it in real tight, till the hammer bounces back off the key, then you know its tight, don't use the hammer with a loose key it will just wear more of the dovetail off apart from being dangerous, (I've sprung our blokes forging away with the key that loose that the top die is clanging up and down loose, "cant you hear that loose die?" "No boss, got my hearing protection in") but I'm going to have to disagree with grant on this one, we make our keys out of something that is softer than the die and the ram, we figure it is easier to replace a key then having to remachine a dovetail, replace a ram or a die. If any thing is to wear 1st you need it to be the key. We have tried hardened keys by the way, and have also had problems with pieces spalling off when driving them in.
Cheers Phil

[JNewman]

I just took the Sow block in to a machine shop to get a slot machined in it. I will borrow my neighbors magdrill next week as soon as the 1.5" Multi-tool drill I ordered comes in. Hopefully I will have the hammer back together by mid week next week.

[Nakedanvil - Grant Sarver]

Forgemaster: "hard" and "soft" are way too subjective. How come my Pepsi gets "warm" when I leave it sit and my coffee gets "cold" when I leave it sit? I've never seen a 4340 wedge spall when tempered to 40Rc. AND ground properly (hemispherical). Properly fitted, neither the wedge or the die/dovetail should "wear". I also am a fervent advocate for lubrication on wedges.

[monstermetal]

I don't know anything but remember a few things I have been told. Tom Clark built his keys out of 6150. Looking it up in machinerys handbook didn't learn me much. It looks like it has properties much like 4140 but has slightly better yeield and hardness numbers The reason he uses it (or did I guess) is because the scale that formed during heat treat has great anti gauld/ lubrication properties. I am with Grant on the heat treated keys. The only wear my dovetails get is from filing out gauld marks. So if you have a alloy or tool steel sow block I would use a soft key to reduce gaulding action. If like me you have a soft sow block then a hard (harder than the matting material 40rc) is the best way to keep wear to a minimum. But like I said just because I think it's the only thing to do doesn't make me right. But I wouldn't use a soft key in any of my hammers even in a pinch because it's the gaulding that hurts the dovetail not the removal of the key sorry for the crappy spelling and grammer. No spell check and hard to use keyboard on my phone

Edited December 4, 2009 by monstermetal

[Ed Thomas]

I'm about to cut the second side of the bottom dovetail in the replacement sow block of my Beaudry. The block is 16" round (close as I could get to the 17" anvil). Since I don't have the original to compare, I've been studying the taper on the smaller #7 Beaudry (200#) which as a 15" anvil/sowblock. On that hammer, the taper over 15" looks to be 1/4".

Does anyone know what the original taper of a 300# should be??? Or have any useful information about this taper? I'm inclined to go with 5/16" unless I hear anything convincing to the contrary. The 1/4" looks too narrow and 3/8" looks awfully wide across 16" for a wedge. I stopped short of initiating the first pass on the shaper because I remember this particular thread and thought I'd ask. You know... circle twice, cut once.

Thanks.
Ed Thomas

[JNewman]

The Massey is 1/8" to the foot which seems to be a common taper. The less taper means a stronger grip and I would assume it would make it less likely to come loose. It does make machining the key a little more touchy as taking a small amount off the key allows it to go quite a bit further into the dovetail.

[patrick]

Ed,

1/8" per foot taper on the keys is what is in my Bradley and this is also the angle on the keys in our steam hammers. If I had to guess I'd go with the 1/8" per foot for your machine too.

Patrick

[Nakedanvil - Grant Sarver]

Here's the best way to measure dovetails. Take two measurements 12" apart. You can't get an accurate measurement anywhere else. Use two dowel pins or pieces of cold drawn or even a couple milling cutters. Can't you measure the wedge? If you're making that too, then you just have to make them match. Usually 1/8" per foot or 1:100 is used in metric. Seen a few that were different, think I ran into one that was 1/4" per foot.

Edited December 7, 2009 by nakedanvil

[John Larson]

My 2 cents: Use of a piece of beer can aluminum as a shim along side the wedge can help hold it and the sow block in place because it fills in the little indentations. I got this from Brian Russell. Soft copper also works.

[pkrankow]

If the keys are inked and fitted I would expect no need for a soft shim.

I have fit a key into an Ajax press flywheel. Took all dxxx day. The person training me milled the keys to near shape, one for me and one for him. I was not allowed to run stationary machines as an "intern". We then inked, fitted, removed, ground the shiny (high) spots down, and started at inking again. Lather, rinse, repeat.

I took about an hour longer to fit a key than the machinist teaching me. The keys were about 10 inches long and roughly 2 x 2 inch, tapered. He finished before me even though he had to cut another key when I started fitting, and his key had funny shoulders in it to accommodate an alignment error.

Since these were in a new flywheel and shaft, we assumed that the surfaces were clean and straight. On a used sow block, would the block's dovetail ever need to be cleaned up? Would this be done in a similar manner?

I'm thinking out loud, I don't have a press at this time.

Phil

[peacock]

Cliffton Ralph solved all my die key problems years ago. Make sure your die and sow block have no depressions in them first. If that checks out. Forge a blank key that is about 1 1/2 times longer than the sow block width. You want 2 or 3 inches sticking out of the narrow side when the die is in position in the sow block the key should be too thick to go thru. the rest of the key sould be close but too narrow. With a rose bud heat about 1 inch of the key next to the spot where it binds up. Put the key into the sow block and die and upset that inch in the cavity. Let it cool drive it out and continue that process an inch at a time untill the whole length is fit. If done right you will be able to see wittness marks for the full length of the key. Make sure you do not have a shoulder at the wide end on the final upset, if so dress with a grinder trim ends to the desired length radius the ends. Make a seperate key for each die. Mark the top so you can put it in the same each time. No ink no mess and your forging not machining or grinding, And they fit. I know it sounds hard but it works and it's not that hard, best key you can have. Phil

Edited December 8, 2009 by peacock
spelling

[SGropp]

The top and bottom dovetails on my Beaudry #7 have a 1/8" per foot taper in the ram and sowblock. The dovetails in the dies themselves are parallel . Both keys drive in from left to right [ facing the the front of the hammer ]

[Ed Thomas]

Thanks, everybody. That is what I needed to know.

Grant: As is normal for the Beaudry at least, there is no key taper in the anvil, and the sow block which would have the key taper was missing, as is the key itself. I am cutting the last of the tapered dovetails in the sow block now. Oddly, the dies were still with the hammer; most likely the sow block got set aside and eventually scrapped. I will be making the key also, of course, along with some of the other missing hammer parts.

Peacock: I like your description of making a key. It certainly makes good sense, as does just about everything Clifton Ralph has ever said about hammers. Thanks.

[JNewman]

I forged and machined the center pin for my hammer today. I ended up having to make the pin offset by about .05". I am not sure why it ended off by that much I think it may have been a couple of things that added up. There was already a shallow hole about 1.25" with mashed corners where I had to drill the 1.5" hole in the anvil, picking up the center of that hole when I figured out where to machine the slot in the sow block was tricky. I got everything back together and dressed the front of the top die a little because the front edge of it was not straight, it was bulged out about 1/16". Tomorrow I just have to grease up the key and reset it solidly.

[John Larson]

Yes, IF machining is right on etc., however the cost of trying a shim of softer metal is near zero and worth a try.

On machining wedges (aka keys), one trick I've learned when an in-process wedge is a bit too thick when trial fitted and needs to advance another inch in its space to be just right, leave the height adjuster of the mill as-is and instead move the wedge one inch in the mill vise. The cut depth will be perfect because the taper of the wedge raises the surface toward the cutter. Same idea works with a surface grinder.

[JNewman]

The only thing about adding a copper shim is I have been told getting the key out with a copper shim can be almost impossible after a while.

[peacock]

I've used alot of copper shims and never had a problem. You need to put them on the side opposite of the die from the key. If the dovetails have holes (low spots) in them you have to be careful not to extrude metal into those holes as it can lock up the keys. Also alot of problems are caused by using too light of hammer to drive the keys out. Light blows from a small hammer will upset the key and not move it. On 25-50# size hammers I use no less than a 5# hammer, as big as a 12 pounder on larger hammers. Hit it hard and square. Phil