Steel Lapping Plate

wagsha48 · Sep 16, 2017

I've been looking for an affordable cast iron lapping plate, preferably 3 of them but have not had any luck. I have a bunch of CRS available so I cut and ground a pair of 4" round steel plates and a 4x6 plate. My question is if these will work for lapping my stones and whatnot? I realize that cast iron is the proper material for lapping do to its greater stability and porous structure for retaining the compound, but these were free.

Can anyone comment on rather or not I can expect these to work? I lapped them to one another from the grinder with 40 micron diamond compound and they seem to work so far. Eventually I might buy a couple flat cast angle plates and convert them if no lapping plates turn up. Anyone know of a good supplier to get them cheap?

AlexO · Sep 16, 2017

They'll work very nicely for lapping small stuff. Up to twice the area of the disks. You want big laps to lap big things, that way you average errors and it doesn't take forever. I'm partial to Al disks - they cut very aggressively with coarser grits. I also use hard wood ones for the coarsest of grits.

wagsha48 · Sep 16, 2017

Thanks that's all very useful info. I've heard of Al lapping for short run applications. Never thought of lapping with hardwood, that might be useful for home projects in lieu of a surface grinder (until I find a cheap one) I might have to give it a try I could have a dozen of them in no time.

CalG · Sep 16, 2017

Wood laps?

wagsha48 said:
Thanks that's all very useful info. I've heard of Al lapping for short run applications. Never thought of lapping with hardwood, that might be useful for home projects in lieu of a surface grinder (until I find a cheap one) I might have to give it a try I could have a dozen of them in no time.

End grain poplar, made up of no larger than 2X2" blocks
Hold the blocks together with strapping, banding, hose clamps or twisted wire. glue too if desired.

AlexO · Sep 16, 2017

wagsha48 said:
Thanks that's all very useful info. I've heard of Al lapping for short run applications. Never thought of lapping with hardwood, that might be useful for home projects in lieu of a surface grinder (until I find a cheap one) I might have to give it a try I could have a dozen of them in no time.

Wooden laps can be easily made to conform to odd surfaces, say a strangely shaped channel etc. They embed the abrasive well and tend to hold it well - bit like a pitch lap for mirrors.

For lapping flats you may wish to consider boring a hole in the middle of your steel laps. Not quite in the center, just a bit off. That helps keeping the lap flat as in the process of lapping loosened abrasive tends to accumulate in the center of the disk and wear it quicker.

rogertoolmaker · Sep 16, 2017

Lapping

wagsha48 said:
I've been looking for an affordable cast iron lapping plate, preferably 3 of them but have not had any luck. I have a bunch of CRS available so I cut and ground a pair of 4" round steel plates and a 4x6 plate. My question is if these will work for lapping my stones and whatnot? I realize that cast iron is the proper material for lapping do to its greater stability and porous structure for retaining the compound, but these were free.

Can anyone comment on rather or not I can expect these to work? I lapped them to one another from the grinder with 40 micron diamond compound and they seem to work so far. Eventually I might buy a couple flat cast angle plates and convert them if no lapping plates turn up. Anyone know of a good supplier to get them cheap? View attachment 208025

Just a comment. The lap has to be softer than the work or the work becomes the lap.
Roger

stephen thomas · Sep 17, 2017

I made some copper laps and some A36 (common "structural steel") laps for honing my carbide scrapers. Copper is a traditional matrix for diamond, but I think the soft steel works as well. As has been mentioned, I've hear aluminum is good, too.

Whatever the soft metal lap, you do have to make a tool to roll the diamond into it. They then cut a long time before needing to be re-ground or re-charged. I use a drop of oil every now and then.

My question is if these will work for lapping my stones and whatnot?

Not sure I understand the question.
Gemstones? As in faceting?

smt

Mcgyver · Sep 17, 2017

I suppose it depends on what the intent is - finish or accuracy (flatness). If flat, i would think the traditional material, cast iron, is attractive because of its stability. Once charged, a lap is a cutting tool and flatness comes from the lap's flatness, so imo you want something that you can get flat and stays put. One of the online vendors used to sell 6" disks of durabar, might be a good starting place. Make one flat lap per grit you'll be using

Just a comment. The lap has to be softer than the work or the work becomes the lap.
Roger

if you are rolling abrasive around between the lap and work, yes. If you are charging the lap and then use it as a cutting tool I'm not sure it matters, although as a practical matter I can't recall trying to lap things that weren't harder than the the lap

wagsha48 · Sep 17, 2017

One lap per grit is an excellent piece of advise. I am looking at an eBay vendor who has almost 1000 6"-8" diameter cast iron/steel/aluminum lapping wafers at $10-15 each.

My need for lapping equipment is not great or immediate I just want something to make sure my honing stones are nice and flat really, but as I continue to expand my knowledge on the subject it seems that with a good supply of lapping tools I may be able to get by without a surface grinder at home. Eventually I'll probably get one for cutter grinding but what I've leared here makes that seem a little less urgent. I can achieve grinding finishes and better with a lap but it doesn't seem like there is any way to get the same level of parrelelism without grinding.

I spent 4 years in college for machining/toolmaking/engineering and never got a single lesson in lapping, not even in the abrasive machining course. Seems like kind of a shame. I am thankful for all the internet has to offer on the subject particularly all the excellent input from the knowledgeable folks here at PM!

CalG · Sep 18, 2017

wagsha48 said:
One lap per grit is an excellent piece of advise. I am looking at an eBay vendor who has almost 1000 6"-8" diameter cast iron/steel/aluminum lapping wafers at $10-15 each.

My need for lapping equipment is not great or immediate I just want something to make sure my honing stones are nice and flat really, but as I continue to expand my knowledge on the subject it seems that with a good supply of lapping tools I may be able to get by without a surface grinder at home. Eventually I'll probably get one for cutter grinding but what I've leared here makes that seem a little less urgent. I can achieve grinding finishes and better with a lap but it doesn't seem like there is any way to get the same level of parrelelism without grinding.

I spent 4 years in college for machining/toolmaking/engineering and never got a single lesson in lapping, not even in the abrasive machining course. Seems like kind of a shame. I am thankful for all the internet has to offer on the subject particularly all the excellent input from the knowledgeable folks here at PM!

Straighten out your "honing stones" on the concrete out at the curb. YOU will never know the difference.

wagsha48 · Sep 18, 2017

I do realize that lapping a hone exceeds the precision required in my line of work. I typically true a hone to another hone and that is fine for me. This is more or less a pedogogical exersize, I prefer to pursue perfection as opposed to settling for good enough. I often wish the guys working for me did the same.

I may not be an old toolmaker but I've spent 11 years in the trade now and have become fairly good at what I do.

AlexO · Sep 18, 2017

wagsha48 said:
I do realize that lapping a hone exceeds the precision required in my line of work. I typically true a hone to another hone and that is fine for me. This is more or less a pedogogical exersize, I prefer to pursue perfection as opposed to settling for good enough. I often wish the guys working for me did the same.

I may not be an old toolmaker but I've spent 11 years in the trade now and have become fairly good at what I do.

"Perfect" is the enemy of good enough. I used to subscribe to that philosophy then I found I was never getting anything done or, when done wouldn't last.

AlexO · Sep 18, 2017

wagsha48 said:
One lap per grit is an excellent piece of advise. I am looking at an eBay vendor who has almost 1000 6"-8" diameter cast iron/steel/aluminum lapping wafers at $10-15 each.

When lapping steel parts you don't need ( or want ! ) to go trough all the grits available like you would do when lapping/polishing optical stuff. Steel is not hard enough, nasty things creep up when grits are too close one to the other one and wastes time like nothing else. I use ONLY 80, 120, 240 or320, 400 and 800. Depending on your source of abrasive you'll find some grits cut slower/quicker or finer/rougher than they should. You should read this once or twice - you'll thank me one day.

The cutting fluid makes a huge difference. I use diesel for finer grits or lapping oil for coarser ones. Car "gas" works the best but the place needs to be cold and humid. I saw some great lapping work done with break fluid but I never tried myself.

wagsha48 · Sep 19, 2017

Whoa the thread has gotten philosophical! Perfection vs. close enough is a topic where I could go for days. I think it's something that must be carefully balanced based on many factors.. but thats another thread, but still a good point.. perfection is an illusion as we surely all know.

Also thanks for reminding me I'm working steel not glass, that being said I'll limit myself to 80,120,240,400,600 and realistically my goal is flat, 4Ra is overkill when 16 is the best I'll ever need

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