Thanks Thanks:  0
Likes Likes:  0
Needs Pictures Needs Pictures:  0
Picture(s) thanks Picture(s) thanks:  0
Results 1 to 9 of 9
  1. #1
    Join Date
    Feb 2008
    Location
    Melbourne
    Posts
    35

    Default Cast Iron - Braze or Silver Solder?

    Hi,

    I need to replace a broken tooth on a cast iron cog in my old Hercus lathe. I intend to mill a slot where the tooth was and insert a piece of cast iron the same width as the original tooth into the slot, then either braze or silver solder it in. I can get some bits from an old cast iron bath to use for the new tooth. Any suggestions on the preferred method?

    I have oxy and have been using it (as an amateur) for over 40 years. I have both plain bronze and nickel-bronze rods and can get silver solder. Which of these would be easiest and/or adequate? If sliver solder is the go, what %?

    From reading other posts here regarding welding CI I understand that preheating is important. What other tricks of the trade are important when brazing CI?

    Buncha

  2. #2
    Join Date
    May 2005
    Location
    Newcastle
    Age
    72
    Posts
    864

    Default

    Braze , I always found tinning flux to work well . Best of luck , cause cast iron is a b1tch to play with
    Ashore




    The trouble with life is there's no background music.

  3. #3
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    57

    Default

    I have seen teeth repairs done just by building up with the brazing rod and machining the new tooth out of the brass. I understand they hold up very well.
    Darrell

  4. #4
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    6,446

    Default

    Brazing for my money


    Use Tobin Bronze braze rods


    Grahame

  5. #5
    Join Date
    Feb 2008
    Location
    Melbourne
    Posts
    35

    Default

    Thanks guys, brazing it is

    I've had a practice on an old cast iron gear, so I'm ready for the real thing now.

  6. #6
    Join Date
    Aug 2004
    Location
    Lost in Space
    Age
    53
    Posts
    331

    Default

    Gidday )

    Read this ....................... haven't seen it put better

    http://www.weldingtipsandtricks.com/...cast-iron.html

    Hope u get from it what i have

    Regards Luke
    Just Do The Best You Can With What You HAve At The Time

  7. #7
    Join Date
    Feb 2007
    Location
    Katherine ,Northern Territory
    Age
    69
    Posts
    736

    Default

    One way is to drill and tap holes along the length of the broken tooth ,then screw threaded pins into the threaded holes ,Then use them as a base to build up with brazing .
    Have done this type of repair a few times on big industrial press gears that take a pounding day in day out .

    Preheat if you are going to attempt arc or mig welding, bury and cool slowly in a lime box or very dry sand .

    Kev.
    "Outside of a dog a book is man's best friend ,inside a dog it's too dark to read"
    Groucho Marx

  8. #8
    Join Date
    Feb 2009
    Location
    Port Macquarie
    Posts
    10

    Default Nickel Bronze tooth

    Quote Originally Posted by Buncha View Post
    Hi,

    I need to replace a broken tooth on a cast iron cog in my old Hercus lathe. I intend to mill a slot where the tooth was and insert a piece of cast iron the same width as the original tooth into the slot, then either braze or silver solder it in. I can get some bits from an old cast iron bath to use for the new tooth. Any suggestions on the preferred method?

    I have oxy and have been using it (as an amateur) for over 40 years. I have both plain bronze and nickel-bronze rods and can get silver solder. Which of these would be easiest and/or adequate? If sliver solder is the go, what %?

    From reading other posts here regarding welding CI I understand that preheating is important. What other tricks of the trade are important when brazing CI?

    Buncha
    Hey Buncha,

    The best way to repair the lost tooth is to build up the area with Nickel Bronze and then machine the new tooth.

    Nickel Bronze is designed for this purpose and in many ways is much better than the cast iron and much easier than trying to use a piece of cast iron as a replacement. Cast iron is tricky material and can come in many forms and hardnesses from soft gray to hard white and black heart. Your gear will be made from gray cast iron and can easily be prepared to take the Nickel Bronze build up.
    You will need some copper and brass flux (303), File the surface where the bronze is to be built up. Don't grind the area as the grinding action spreads the graphite from the cast iron across the surface and intergranular penetration won't take place and the tooth could release from the gear.
    Preheat the whole gear prior to braze welding to a temperature where some flux when sprinkled on the area to be brazed changes to a liquid.
    Be careful not to overheat the area and the flame should be applied and removed frequently when building up the area, the reason being that 1) the bronze will run out of the area, 2) overheated bronze will fume indicating that the properties are being burnt out of the bronze 3) overheating the cast iron prior to welding will oxidise the surface of the cast iron and intergranular penetration won't take place. I have alwaays found great success repairing gear teeth using this method. Contact me if I can be of any further help. Regards Ted.

  9. #9
    Join Date
    Feb 2008
    Location
    Melbourne
    Posts
    35

    Default

    Hi Ted,

    Thanks for that. I heated the gear in the oven to 270 C (lovely smell of hot oil in the kitchen ) then used nickel bronze as you suggested. After it was cool I cut a slot either side of it, then filed the tooth profile on. Before starting I had made a profile gauge by putting a blob of Polybond bog over three good teeth. I used this as I was filing to check position and profile. Once it looked good with that I got the mating gear and ran it over the repaired area by hand to see if I could feel any problems. It was fine, so I reassembled it to the lathe. It ran perfectly with no change in the gear noise as the new tooth was engaged.

    Thanks to all for their advice.
    Buncha

Similar Threads

  1. Silver Solder Pt 2 How to
    By Grahame Collins in forum METALWORK GENERAL
    Replies: 0
    Last Post: 11th Jan 2007, 10:51 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •