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  1. #21
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    Found a video ... they were like this, but smaller and simpler. And made in the US ... same principle tho. Any other old codgers remember the brand and model ?

    Centerless Lap

    Lucky day, found it

    Spitfire

    I heard Fritz died ? He always had decent stuff ...

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    Good morning athack:
    This is super interesting, and quite unexpected.
    I've always taken it as gospel that the lap must be a different material and softer than the workpiece so the abrasive grains preferentially embed into the lap and to forestall the possibility of galling.
    All the reading I've ever done makes some variation of this claim, so I learned something new today and I thank you for that.

    So why is this true...is it something about the porous microstructure of cast iron that makes it work so well?
    Does it have other desirable properties?

    I know machine slideways are often cast iron but they are not supposed to wear and of course they will pick up if they are starved of lube.
    The idea that the lap may be allowed to wear at the same rate as the workpiece so both become geometrically better is new to me...I always thought of only the workpiece wearing and not the lap.

    So is it true that the geometry of the lap ALWAYS wears in so both conform together over time, or is it a special case when it's cast iron against cast iron?
    I assume a plated diamond lap does not work this way...so how do they work?
    Should they even be called laps or is that a misnomer?

    Much to learn...I appreciate your contribution to the subject, so thank you in advance.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

  3. #23
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    Quote Originally Posted by implmex View Post
    The idea that the lap may be allowed to wear at the same rate as the workpiece so both become geometrically better is new to me...I always thought of only the workpiece wearing and not the lap.
    Hypoid and spiral bevel gear sets are lapped to correct tooth geometry after heat treatment. The goal is to reduce gear mesh noise and improve load capacity. The process involves either lapping the two hardened gears together or using a master cast iron gear with the individual hardened steel gear.
    The lapped gear pairs must be used as a matched set. The gear lapped using a master cast iron lap does not need a matched gear to complete the pair.

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    Hi Robert R:
    So the logical corollary to your example is that when it's a cast iron master used as the lap, there is no appreciable wear on the lap, whereas when the gear pair is run together with abrasive, both wear equally and will only mate correctly as a pair because of that.

    So there are two kinds of lapping with two different consequences.
    Very interesting!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post

    So there are two kinds of lapping with two different consequences.
    Very interesting!

    Cheers

    Marcus
    Hi Marcus,
    Yes, two versions of lapping - loose particle, and embedded. The sort of lap that has been discussed here is embedded, either due to softness of the lap itself, or with a harder lap that's had abrasive purposely pressed or rolled into the material to affix it.

    For an example of loose particle lapping, check out this video: YouTube

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    Quote Originally Posted by athack View Post
    The thing that concerns me the most is the segmented idea. Lapping works by wearing the lap and work piece therefore making each very round and straight.
    thanks. I agree, I've not done it for decades as it sounds like you have, but I've done some and have got great results, both inside and outside lapping. Lapping in the round, where expect the lap to worn is different than flat lapping where you charge the lap - the abrasive particles on the surface act as a cutting tool and the lap isn't touched There is a certain logic to it - so long as each part of lap covers each part of the work. They can't but wear into near perfect cylinders. There's still the possibility of a banana resulting from clearance, but with fine compound that error is going to be very small. In a recent project I lapped a 40mm and got a consistent diameter to a micron over 10" using a indicating mic. I've also done lots ID lapping, both always with the work turning and lap floating, handheld.

    If your work is hardened, I agree with cast iron, but I'd be concerned using it with mild steel. With the loose abrasive, the cast iron should be able to press it enough to embed into the soft steel work piece, no?

    what do I know compared to some one who's being doing for 40 years....but following a few basic principles its always worked. It seems to let one get pretty incredible results with fairly simple equipment






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    I find lapping to be fun actually.Need some advice on lapping OD I had to take a crash course in lapping OD as I had turned my cast iron reaction carrier in my Turbo 400 racing trans on my old South Bend 10k. This is the finish out of the trans.

    I found out real quick how the clamping band “hardened” 3 sections of the cast Iron so the turning process left low and high spots. I decided to try out my custom due grinder tool holder and grind the hard spots- a hard lesson on a fools errand!! Now I know why you need electric motors with speed controllers to do od grinding!!



    Anyway it left a horrible finish. Coincidentally I had just watched a Suburban Tools video on od lapping. Don mentioned American Lap so I went to their site and learned things. I decided to make an od lap. The reaction carrier is about 5.875” if I remember. I made the lap from 1” thick aluminum flat stock bored it on the lathe then turned the od. I drilled relief holes evenly around the id and cut slots with the band saw. I added a set screw to keep the lap ring from turning inside the clamp. Next I turned a lap ring that fit between the lap clamp and the reaction carrier. I put an angular slit in the lap ring.





    I used Clover 180 grit Silicon Carbide lapping compound. I didn’t make a handle to hold the lap assembly- I definitely should have!! I used a Vise Grip plier to hold the lap- it worked but the unexpected torque definitely caught me by surprise!! In process photo.



    Finished reaction carrier. The lapping trued the hard and soft spots to the same diameter. There was no taper front to back-only 3.500 inches long. I checked the od on the surface plate with a thou indicator-true round. Granted the reaction carrier gets grabbed by a band so it doesn’t need to be super tight tolerance but roundness and finish was important for the style band I ended up using. Was a good size learning curve but the reaction carrier was saved and made better than when I started.Need some advice on lapping OD





    Sent from my iPhone using Tapatalk

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  10. #28
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    Quote Originally Posted by Robert R View Post
    Hypoid and spiral bevel gear sets are lapped to correct tooth geometry after heat treatment. The goal is to reduce gear mesh noise and improve load capacity. The process involves either lapping the two hardened gears together or using a master cast iron gear with the individual hardened steel gear.
    The lapped gear pairs must be used as a matched set. The gear lapped using a master cast iron lap does not need a matched gear to complete the pair.
    Some slight additions and corrections ... automotive spiral bevels were commonly lapped for noise reasons. They also reciprocated the parts, because you can't just lap gears together, it destroys the geometry. Teeth push against each other a lot over the entry stage, then roll more through the middle stage, then wipe across each other in the same direction on the exit stage. So lapping destroys your tooth shape as the amount of motion changes across the position on the teeth. If you don't take additional measures, such as reciprocating the parts across each other or creating a sideways action, then the tips and roots wear more than the middle during lapping.

    There were also spur and helical gear lappers made by Red Ring that used the crossed-axes principle for the same effect. When you mesh a helical gear with a spur gear, for example, there is a sideways motion to the meshing action that is supposed to do the lapping. Those lappers use cast iron laps and loose abrasive, easy to make, but they wear out. I used to get barbell weights from Dick's Sporting Goods to make the laps, worked tits You don't have to keep the sets in pairs as you do with automotive spiral bevels.

    I've never heard of using a cast iron master lap with spiral bevels but it's quite possible, I'd guess more in the cases of smaller parts ? Like sewing machine gears ?

    btw, they don't do that anymore ... at least not in volume production. A current Gleason production set will have cnc roughers and finishers and a tester all networked together, so that the settings can be adjusted on the fly to compensate for optimal tooth shape and heat treat distortion. That's the big one, heat treat. I believe they don't even use quench presses anymore, and they cut dry now.

    Times change

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