Making of a flat lap.

[justin1]

I figured it would be nice to be able to lap small objects and make them look more refined and shinny.

So I dug a piece of scrap cast iron out of seacan and looked around all my random cut offs of stuff I've collected and found a suitable piece of aluminium for the 3 flat surfaces I need to make a super flat lap.

The cast iron was simple enough just milled it flat on both sides and used boring head to cut some groves in it and voila base for a lap complete.

The aluminum was already grooved and milled on both sides so was ready to go.

The next thing I did was surface grind a face of the cast iron and then both sides on chunk of aluminum, which wasn't as easy as cast but still came out good. Trick was too dress the wheel alot and only take couple thenths at a time.

This is were I got too today. I'll work on lapping it in the course of a couple days probly and see what happens and then post the results.

Wheel flavor I used to both cast and aluminum seemed to work ok but probably isn't the right choice for aluminum if I had to guess.

Any tips for lapping let me know I'm just gonna watch few YouTube videos and go ham.

 

[jorogi]

Tom Lipton has a good vid.

 

[justin1]

Tom Lipton has a good vid.

Funny enough I'm currently rewatching his vids about lapping as I remember seeing them in the past

 

[justin1]

Did some lapping today with cast iron and aluminum and didn't like how it went so scrapped the idea of using aluminum and hunted around for some more cast I could lap with, ended up cutting up what was left of a table saw extension that was broken.

Ended up with two useable chunks of similar size but only around 8"x4" for one and 7.5"X5" so hopefully these will work. not idea but all I had on hand for suitable cast iron. So I'll try agian to lap the the 6x6 lap and see how it goes tomorrow when I get some free time.

 

[6.5 Fan]

I like your shop shoes, i wear the same ones.

 

[Mcgyver]

Any tips for lapping let me know I'm just gonna watch few YouTube videos and go ham.

I don't know what you know, read or have seen so apologies if I'm preaching to the choir. For posterity here are some very basic points. (I'm the one cringing when I hear of someone throwing abrasive in between two work pieces and calling lapping lol)

Flat lapping is a little different than in the round - in the round, its self correctly and loose abrasive is ok/used. i.e. roundness doesn't come from how round the lap is. With flat lapping, flatness comes from the lap. You start with something surface ground or scraped very flat. I wouldn't not try to use the three plate method. It works for lapping granite that doesn't embed, but for metal, scraping is the way to go (for the three plate method), else you know don't know where you are. i.e. one plate gets embedded more than the other so cuts more etc. Even without that concern, with scraping, you have a feedback mechanism - the spotting. What do you use for lapping? Wouldn't you need an autocollimator or interferometer to assess progress?

It should end up be very flat with a good surface grinder or as good or better scraping into a Grade A plate. You'll not get it any flatter by the three plate method (scraping), it's just an exercise to prove Whitworth was right. It's not necessary or reasonable to try and work to a tolerance flatter than a grade A plate. I've heard many keen protagonists threaten to scrape a plate by Whitworth's method, but not heard of a follow through to completion or seen results presented. It's too much work compared to buying a good surface plate and scraping, or trusting the flatness of your grinder. The finish you get on the work is a function of the fineness of the abrasive, not the flatness or finish on the plate.

The flat lap is a cutting tool. You charge it by pressing abrasive into its surface with something harder than the plate material. I use a ball bearing held in a vise grips for example. After charging, you wash as you don't want any loose abrasive cutting or abrading the lap. Cast iron is ideal, but I've used a small piece of aluminum (quick and dirty diamond lap for lapping carbide to prepare for silver soldering)

You have to recharge the lap occasionally, but its stays flat and perfect for ever as the work never touches it - the work is riding on the embedded abrasives. i.e. This cast iron lap below has been in use for about 20 years. The surface is the same as the day it was made and will never wear.

As the lap is a cutting tool, charged with a particular size of abrasive, make separate laps if you need several types or sizes of abrasives.

You can cut into the diamond pattern sometimes seen. It can help with stiction and give the dirty oil somewhere to flow, but isn't' imo really necessary. It would make scraping a miserable job, and I wouldn't do it after scraping (or grinding) as you change the equilibrium of forces and likely the flatness.

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[justin1]

I like your shop shoes, i wear the same ones.

Thanks bad habit but nice and comfy I got crock patterns in some of my socks from welding.

@Mcgyver

I don't have autocollimator yet it's on my wish list just not sure what to get yet. and don't know anything about interferometer.

I would say my lapping knowledge is limited not something I've haven't read up on much it's more something I'm curious about and no projects currently require lapping. Just happen to have a lap shaped piece of scrap and figured it would be interesting to experiment on.

I'm better at hands on learning as I find alot of technical side of flatness and machine rebuilding very dry to read about. I much rather dick around on something I'm willing to scrap and make my mistakes on stuff that doesn't matter.

I'm using non charging abrasive ATM but I do have some 12 micron diamond I was gonna charge it with once it was "flat"

I have a 2 B grade plates one is 12x18 and other is 28x36 and a cast iron plate of unknown flatness and a block of granite from what think was a measuring instrument which I think maybe the only A grade thing I have besides 3" optical flat.

I'll finish my thoughts after concrete floor is poured today as I'm currently waiting for truck to show up. So have a few minutes before the fun begins.

Edit.

Grade A block maybe

I got a scrapper too but no way to sharpen yet so I've been delaying playing with it till I make a slow speed grinder kinda like the one you made. It's on the menu just haven't sourced piece of cast for it yet got the motor 1725 1ph 1/3hp heavy duty motor

 

[Mcgyver]

I don't have autocollimator yet it's on my wish list just not sure what to get yet. and don't know anything about interferometer.

That was meant as rhetorical, i.e. having either would be the exception which is yet another reason why the three plate method makes no sense vs buying flatness (a surface plate).

For just playing around and getting started, get a piece of cast iron and scrape it to one of the plates. You'll learn and it will be a useful lap when done. Until I see the electron microscope results I'm somewhat dubious on the non embedding. I get that it breaks , but how soon, none of it embeds?

Is the scraper carbide or steel? You can sharpen a steel one on a stone. Bit of a pita but it works. Presumably you could do the same with carbide on a diamond stone. Pretty soon though, you'll want a power lap (the one I made is based on a cheapo Canadian Tire grinder). It does NOT have to be low speed. Low speed grinding is for diamond abrasive on steel (slow so diamond is not absorbed) or any abrasive on tool or carbon steel so you don't hurt the temper ... however diamond on carbide can be done at full speed. The wheel does not have to be flat, lathe turned is fine - in the case you are using the lap for finish, putting an edge on, not for flatness.

There used to be some business, maybe Little machine Shop(?), selling 6" cast iron disks for reasonable dollars. There is always McMaster Carr. Just checked, they are 43US$ for 6x1". Not cheap, but not outrageous

The basic act of scraping, creating flatness, is 1/2 an hour of instruction, if that. It's all the auxiliary stuff that makes it more complex, how to make scrapers, how to keep them sharp, how scrape things square, parallel, to a specific angle, mating parts, alignment etc

 

[justin1]

.

The scrapper is carbide, and as for cast iron I got a small load of scrap steel I got to drop off and was gonna see if scrap yard had any useable chunks of iron laying around. I do have a cast iron counter weight from forklift I want to cut chunks out but been pre occupied with shop so a lot projects are kinda on the back burner ATM.

The scrapping part I think is straight forward it's the rest of it that like you say is complex. It's one thing to visualize the concepts and another to actually put into practice. The first real scrapping project is probly gonna be the compound on the big lathe as it's more of a stand alone part and I feel like a good place to start as it is smaller and it has a few of the principles alignment/geometry.

This is after I make some straight edges and some of the other tools I need to even start scrapping.

I have a extra bench grinder laying around would a diamond resin wheel like this one be good for one side then just a lap on the other side?

Resin wheel

And it would be easy enough to convert for use as a side wheel type tool grinder.

 

[justin1]

I did about 4 blind scrapes in 45 pattern after surface grinding then probly 5 or so more bluing after that to get to here. The flatness is probly the work of the surface grinder vs me lol.

I don't know how I feel about my current scrapper blade It. I find it hard to aim and easy to gouge the corners of insert into piece. I do remember reading about people not liking the geometry of factory Sandvik stuff but I'm thinking I just suck and that's probly half the battle.

Guess I need to get on a few projects so I can make some various sized scrappers and radius and see what I like.

But from the pattern I'm see I looks like I need to work around the outside and ignore the middle for now. Not sure if I can get the PPI up with current scrapper but maybe with small one I could start aiming for higher PPI after next couple passes. Would be my guess.