Lapping It Up: Setting up for precision hand lapping

In which we learn about making and using cast iron laps and diamond slurry to achieve high finish and high accuracy surfaces in hardened tool steel. And have fun doing it.
Robin Renzetti: ‪@ROBRENZ‬ on YT and / robinrenzetti
Tom Lipton: ‪@oxtoolco‬ on YT and / oxtools
Adam Balogh: ‪@laneymachinetechclassroom‬ on YT and / laneymachinetech
Referenced videos:
Tom Lipton: Making Flat lapping plates 1 - • Making flat lapping pl...
Tom Lipton: Making Flat lapping plates 2 - • Making flat lapping pl...
Tom Lipton: Making Flat lapping plates 3 - • Making Flat lapping pl...
Robin Renzetti on the PFG Live, on lapping: • PFG IG Live 2022 0410 ...
Adam Balogh on the PFG Live, on lapping: • PFG Live 2023-0115: La...
McMaster-Carr:
The Cast Iron plates - www.mcmaster.com/8588T23/
Hyprez Diamond Lapping Slurry, 3 micron: www.mcmaster.com/4857A47/
---
ERRATA:
Robin Renzetti (‪@ROBRENZ‬ ) makes a very good point:
"Remember that the straight band only shows "straightness" not flatness. You must align the bands a second time 90° to the first to access straightness in that direction to determine "flatness".
Only one reading is like using a repeat o meter on a surface plate oriented parallel to one side only. The flat is showing all the information in one orientation but curvature 90° to the bands registers as variation in band spacing which is not easily discernible by the human eye."
Thank you, Robin!!
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Links for products/designs mentioned are at pfg.gg/links
Follow me on Instagram at "spencer_webb_nh".
("PFG Stones®" is a registered trademark of Kinetic Precision)

[@johnyoungquist6540]

Inspired by Tom Liptons 3 plate video I bought 3 8 inch rounds from MCmaster turned them round and flat. Then ground them flat. Then made a plate holder for my CNC mill. I programmed the grinding motion and went through several grits using the 3 plate sequence. Hours of grinding was done I used a combination of linear and rotary motion. The results were extraordinary with no hand work. Using the CNC machine is well worth it, In high school I made a telescope mirror but made a grinding machine first. Just lazy I guess.

[@KPNH]

Brilliant!!

[@jacquelinesears1770]

i have been looking for a good explanation of reading what the optical flat is telling me that was the hands down best one period thank you

[@KPNH]

Glad I could help!

[@cylosgarage]

Wonderful lapping content aside, super impressed by that dbit cutter! Didn’t look like there was hardly any burr at all

[@KPNH]

Thanks! Yes, that cutter did a great job.

[@JohnGrimsmo]

Absolutely fantastic Spencer, thank you!

[@KPNH]

Thank you, sir!

[@AlmostMachining]

Great job Spencer !!!

[@KPNH]

Thank you, sir!!

[@ronwhittaker6317]

Love Robbin silly

[@Flatlapper]

Hey there, just found your channel. Right up my ally. Not a ton of good lapping explanation content out there. The Oxtool series was quite good. It's great to see some new stuff being posted ! I'm looking forward to following along. keep up the great work Sir!

[@KPNH]

Thank you! Welcome aboard!

[@geckoproductions4128]

thanks for the explainer about optical flats

[@KPNH]

Happy to help!

[@WallaTool]

great video! lol nice intro

[@rusmooseos976]

So nice, ussr glasses =) beautiful

[@KPNH]

Thank you 🤗

[@chrisj4570g]

I played bass for Lap It Up.

[@KPNH]

Remember the hit song "Baby Embed Your Diamonds"? Good times.

[@dimsum5567]

Amazing optical flats from the USSR with a quality sign 😂

[@KPNH]

Bought those a while ago on eBay. They're good.

[@user-rw7xn3fo1t]

Nice work. What was the angle of the d-bit cutter and how deep/far apart are the grooves?

[@KPNH]

I believe 30-degrees, 0.03" deep and 0.25" spacing. It's not critical.

[@PaulMorley1]

Spencer, just to confirm I have it. 2 things... Instead of 3 plate method to maintain flatness of laps, use 2 plates + periodic measurements. Lap on bottom plate but when convexity or concavity is measured, flip the plates and condition until measurement is same/flat on both?? As for the diamond slurry, based on the above will you essentially now dedicate 2 plates for each diamond grit size due to grit contamination?

[@KPNH]

The "three plate method" refers to auto-generation of flatness, and also calibration. But, maintenance of laps is a two-plate system. The "bottom" plate tends toward a convex shape, while the conditioning lap on top becomes concave. Without trying to go into details, that allows you to drive the work piece toward concave or convex as needed and observed by measurement. Yes, I dedicate a pair of laps to one diamond size.

[@emislive]

Nice work! This better illustrates what Robin was talking about with two plates in use. Without a decent surface grinder to get close enough, it still seems one needs to start with the three plate method. Is there a controllable way to go from the lathe to flat enough to lap using only two plates and no grinder? Also, aren't you committed to the coarsest grit you used? I expect some diamond would embed into both laps when conditioning with the 3μm slurry. The abrasive will degrade over time, but one stray particle can create scratches when moving to the finer grits. Looking at how straight those lines are, I think you are seeing real wringing! Wringing is supposed to work without oil in vacuum. Do you have a vacuum chamber handy?..

[@KPNH]

Thank you! 1) Yes, see Tom Lipton's video(s) via the links in Description. He uses only a saw and a lathe. 2) Yes, embedding is an issue. My plan is to dedicate a pair of laps to one size/type grit. 3) I do have a vacuum chamber, but I know what *real* wringing feels like and I think I need to lap at a finer grit. That is why I just got five more disks to make lapping plates. I will be able to have 3-, 1-, and 0.25-micron dedicated sets. Good gage blocks, cleaned on a PFG Stone will wring like crazy. I want to achieve that.

[@Sleepingsaloon]

@@KPNH any issues with diamond embedding in the A2 discs?

[@KPNH]

None. The rule in lapping is that the lap is softer than the work. This is why. The A2 was RC 55 to 62. My dirty little secret is that these discs were part of a six-disc set where I was really testing tempering temperature vs. hardness. Note the four hardness test point visible around the stamped numbers. After that they were used for my "five disc" test on the grinder chuck. Now they are the lapping test subjects. Re-use, Recycle, people!

[@ashreid20]

@@KPNH is there any hope cleaning the plates of embedded particles? I read somewhere about using an ultrasonic bath. Or do you think that is a fools errand? Also, I'm struggling to find water soluble slurry, I can only seem to find the sringe of oil based diamond paste. Do you you have any experience/comments on the difference? (If this covered somewhere else, just point me there)

[@ashreid20]

I should have said: Oil based diamond paste and scallion carbide powder and im in the UK

[@ParallelTransport]

Given how cheap USSR flats are and how expensive monochromatic sources are, do you have any advice on budget-friendly light sources for the home gamer?

[@KPNH]

Seek the Monochromatic rabbit hole at pfg.gg/links

[@ParallelTransport]

@@KPNH Thanks! Looks like it'll be interesting reading!

[@howtoguro]

I’ve tried running a laser through a marble or something that spread the coherent laser and that works pretty well.

[@ParallelTransport]

@@howtoguro Yeah that's kinda what I've been thinking. My biggest concern is how to know if you've spread the laser light enough to be safe. But I'm pretty conservative with regard to injuries, especially with my eyes.

[@howtoguro]

@@ParallelTransport You could just wear laser shades. Even really typical clear safety squints provide some protection against lasers. Full nuclear mode would be to view it from a secondary camera and monitor. Sadly, powerful lasers are too common. I actually bought a red laser point for a “Cat Toy” because I figured it would be weaker, but it was a class 3R so be really careful.

[@travisgilbert3290]

what pen is that near the 8 minute mark?!?!

[@KPNH]

That, sir, is a Saga by Grimsmo Knives!

[@causeitso]

Good video but I suspect these plates are only locally flat. They are as flat as the rails in your surface grinding machine.

[@KPNH]

All flat is local.

[@jacquelinesears1770]

I am lost a little bit on round or square plates some how are different ??? The photo is my wife its her account

[@KPNH]

It's really about the symmetry of the rounds simplifying the behavior.

[@jacquelinesears1770]

So as a person who has spent a life time grinding steel square and flat that's hard for me to swallow that doesn't sound like engineering @@KPNH

[@KPNH]

If you want to make square plates, have at it. Please make a video about it. I am interested.

[@SergeiPetrov]

Probably with an abrasive of this size (even in water) you should not contact with your hands? I wish you good health.

[@KPNH]

I wear gloves.

[@robertfontaine3650]

I hate people with surface grinders and full size tools.

[@KPNH]

I'm sorry. If you watch through the wrong end of a pair of binoculars, you may feel better.

[@chronokoks]

Hyprez.. not Hyprex.. you got the labels in front of you dude...

[@KPNH]

You are completely, totally, almost otherworldly correct.