Lapping a small steel (hrc 56) part to flatness and mirror finish.

[Nobby]

Pitch lapping has its own challanges. The pitch acts as a really thick fluid. If the pitch sits a couple of weeks (between lapping jobs), it won't be flat anymore. In contrast to the metal or epoxy discs.

Huygens Optics has an interesting video on the subject. He jump starts a non flat pitch disc with a 2000 Watt paint stripper. After that he achieves flatnesses under 100 nanometer. Insane!

Thanks for watching my video - and thanks for the compliments.

 

[MCritchley]

I want to re-emphasize that when you use the rolled-in method of charging a cast iron plate with diamond, you clean off all loose abrasive and paste. Wear on the plate is minimal. We've been using the same plate every day for several years and I haven't had to regrind or surface it yet. It's important to brush/wipe the plate frequently to prevent clogging and crud build-up. Pretty sure we use 9 micron diamond, but I'd have to go look to be sure.

Do you use a lubricant when lapping with your charged plate?

 

[Conrad Hoffman]

We use our plate dry. Typically we're touching up contact points on small hard anodized aluminum parts.

 

[luke8888]

My previous tests were all about flatness, but with functional parts things being parallel and square is often very important too.

Does anyone have tips for lapping parts parallel and square?

I have some (yet untested) ideas. The main is to check the parallelism/squareness very frequently and put more pressure on a side of the object that needs more material taken away. Is there anything else that might help?

 

[Conrad Hoffman]

I believe there are fixtures for planetary lapping machines that keep the parts parallel, but for manual lapping I just do what you're doing.

 

[machinistrrt]

You might want to check out the homebuilt reflector telescope folks. They make their surfaces to a precise curve well below the Rayleigh (sp) limit by hand, using a plate glass tool. Info online and books.

 

[luke8888]

You might want to check out the homebuilt reflector telescope folks. They make their surfaces to a precise curve well below the Rayleigh (sp) limit by hand, using a plate glass tool. Info online and books.

Thanks, indeed I did. There is lots of good information there. For others interested I recommend this youtube channel https://youtube.com/@Opticsed

 

[machinistrrt]

Thanks, indeed I did. There is lots of good information there. For others interested I recommend this youtube channel https://youtube.com/@Opticsed

Thanks for the tip- never thought of youtube. The reference I used was a book (

How to Make a Telescope ( Second English Edition) ).​