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Looking for the right mill bit

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
It is a BTI 925 hammer.
You can see in the picture that I have a bit of bad surface right where I need an o ring and back up ring to sit for the valve body.
I took it to a machine shop for the same problem a few years ago. I think you can see where the repair was made in the picture.

I think I just want to do it myself this time. I'm looking for suggestions on rod type for the fill and the right type of mill bit to flatten it back out.
The damage ring is pretty close to 60mm.
 

Jonas302

Senior Member
Joined
Jan 4, 2015
Messages
1,197
Location
mn
Hard to tell from the pic but I was wondering if it would be feasible to take the entire surface down without having the weld buildup ?
 

digger doug

Senior Member
Joined
Nov 2, 2011
Messages
1,371
Location
NW Pennsylvania
Occupation
Thrash-A-Matic designer
It is a BTI 925 hammer.
You can see in the picture that I have a bit of bad surface right where I need an o ring and back up ring to sit for the valve body.
I took it to a machine shop for the same problem a few years ago. I think you can see where the repair was made in the picture.

I think I just want to do it myself this time. I'm looking for suggestions on rod type for the fill and the right type of mill bit to flatten it back out.
The damage ring is pretty close to 60mm.
Are you asking for a spotface tool ?
 

DMiller

Senior Member
Joined
Feb 21, 2010
Messages
16,430
Location
Hermann, Missouri
Occupation
Cheap "old" Geezer
Will need a form of Fly Cutter or a lathe bit holder if intend to flat mill those faces unless do find a way to Face Grind off a holding fixture.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
Hard to tell from the pic but I was wondering if it would be feasible to take the entire surface down without having the weld buildup ?
The groove on the face is pretty deep. That is a lot of metal to take off. And the face is hardened steel.
Just did the disassemble yesterday morning and haven't had a chance to contact any machine shops. But when I had it repaired before I had contacted every machine shop on my island and only one place was even willing to try. And they found out that they (it was a while ago so I don't really remember). Either found out that they couldn't cut it or that the piece was too big to mount on their mill. So he did the weld and then somehow cut it flat.
I don't know what material he used for the fill. Just looking at it I would guess a nickel alloy but that is just a guess.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
Are you asking for a spotface tool ?

Will need a form of Fly Cutter or a lathe bit holder if intend to flat mill those faces unless do find a way to Face Grind off a holding fixture.
I was looking at both. And there were a few more I found online that were similar but had carbide inserts that ran only in the last half inch of the tool diameter.
As far as a holding fixture; I was toying with the idea of using my mag drill. But this is all new territory for me, I don't know what the speed requirements are for any of these mill tools when dealing with hardened steel.
 

Jonas302

Senior Member
Joined
Jan 4, 2015
Messages
1,197
Location
mn
Your mag drill is not going to like any kind of face cutter If I really had to do it with a drill and I have done a lot with them it would have to be a homemade flycutter that used the bore as a guide to hold in place it would have to be made on a lathe for a tight fit

I think your current best bet with no machine tools would be to fill the groove with silver solder, or brazing rod and file it down with a nice wide flat file to make it flat again
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
As in a Head or Block Milling setup where a Grinding head not milling bits are used.
Your mag drill is not going to like any kind of face cutter If I really had to do it with a drill and I have done a lot with them it would have to be a homemade flycutter that used the bore as a guide to hold in place it would have to be made on a lathe for a tight fit

I think your current best bet with no machine tools would be to fill the groove with silver solder, or brazing rod and file it down with a nice wide flat file to make it flat again
Guys I really appreciate your help with this. Especially since I don't seem to even speak the same machining language as you. Honestly, every time I get a reply I have to Google the tool you mention before I reply.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
Alright. I have had a few moments and a glass of bourbon to compose my thoughts.
It seems to me that my best option for a permanent fix is to send the damaged section off island to a shop that can both cut out the damaged bit and then reharden the piece. The downside is that means weeks of down time for the hammer. Another downside is that my go to shop for that sort of work was Ramco in Washington. And they closed shop earlier this year.
The other best option is to replace the entire section of the hammer by buying it from the dealer. The downsides there are the price tag and the fact that BTI is now Striker. And I have been underwhelmed with the quality of Striker replacement parts.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
Alright. I have had a few moments and a glass of bourbon to compose my thoughts.
It seems to me that my best option for a permanent fix is to send the damaged section off island to a shop that can both cut out the damaged bit and then reharden the piece. The downside is that means weeks of down time for the hammer. Another downside is that my go to shop for that sort of work was Ramco in Washington. And they closed shop earlier this year.
The other best option is to replace the entire section of the hammer by buying it from the dealer. The downsides there are the price tag and the fact that BTI is now Striker. And I have been underwhelmed with the quality of Striker replacement parts.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
So, unless the client is agreeable to the downtime; I am down to field repair.
Here is where I get a bit confused and look to you guys for advice.
When I look at the damage, I think that the previous repair media was too brittle. In my mind that means too hard. At the same time... I also suspect that silver solder or brazing rod might be too soft.
But perhaps the soft touch is the way to go.
I had a very similar problem with an NPK hammer around the same time. But it was the hammer side that took the seals on that one so just the valve body needed to machined.
 

Mobilewrench

Senior Member
Joined
Feb 26, 2020
Messages
373
Location
Kona, hawaii
Hard to tell from the pic but I was wondering if it would be feasible to take the entire surface down without having the weld buildup ?
I see that more than one of you mentioned grinding it down on a mill. But Jonas302 was first.

So, I just welded up the groove and made it flat again. Lasted until last week. Now the ring is pitted out again. And back in my lap. There still isn't a machine shop on my island that will touch it. And three on the mainland said they wouldn't either.

I do think that the best option is taking the pitted surface down. But why won't anyone do it? If Ramco was still open, I would just ship it to them. They said they could do it when I was trying to figure out my options four years ago.
Also, I am not sure about the hardening of the material. Are hammer bodies made of a harder alloy of metal or are they heat treated for hardness like the pistons, bushings and tools?

Anybody knows of a shop that will take this on, get me in contact.

I have a couple of spit ball options to throw out. First is the idea of machining down the valve body so that the o ring and back up ring have more protrusion to press into the damaged area.
Next one is perhaps making something similar to engine fire rings.
Thanks in advance.
 
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