Author Topic: Lapping  (Read 1590 times)

Offline mm289

  • Jr. Member
  • **
  • Posts: 27
Lapping
« on: January 04, 2018, 05:52:32 PM »
 :scratch:sounds like scraping, just spelt differently :)

Wanted to lap in the bottom of some surface gauges and stuff, wondered what the approach was? Saw Pete do it on the course with some of the lapping powder Matthew brought and a surface plate...

What/where for the lapping powder, does it ruin the surface plate, could you use something else etc etc.

Any ideas?

Cheers,

Paul.

Offline mattinker

  • Hero Member
  • *****
  • Posts: 1107
  • Country: fr
Re: Lapping
« Reply #1 on: January 04, 2018, 09:58:09 PM »
Paul,

What Pete used was diamond flour, on a surface plate. The plate will be impregnated with diamonds, You'd have to at least re-scrape to use for anything else. The other alternative is 3000 grit wet and dry paper on a surface plate. If you can completely cover a small surface plate with the wet and dry, you should be able to use it without wearing down the plate. (See Tom Lipton's video Reconditioning and calibrating a surface plate, the technician mentions this at one point)

Cheers, Matthew

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6413
  • Country: gb
  • East Sussex, UK
Re: Lapping
« Reply #2 on: January 05, 2018, 02:59:56 AM »
To save your surface plate get your local glass shop to cut you a piece of their thickest plate glass and use that to back your wet and dry paper. You'll find the plate glass is plenty flat enough over the short distance we are talking about.
Andrew Mawson
East Sussex

Offline mattinker

  • Hero Member
  • *****
  • Posts: 1107
  • Country: fr
Re: Lapping
« Reply #3 on: January 05, 2018, 06:07:25 AM »
Paul,

What Pete used was diamond flour, on a surface plate. The plate will be impregnated with diamonds, You'd have to at least re-scrape to use for anything else. The other alternative is 3000 grit wet and dry paper on a surface plate. If you can completely cover a small surface plate with the wet and dry, you should be able to use it without wearing down the plate. (See Tom Lipton's video Reconditioning and calibrating a surface plate, the technician mentions this at one point)

Cheers, Matthew

I forgot to say, use paraffin (Kerosene), white spirits, WD 40 or some thing light works better than dry!

Andrews plate  glass method works extremely well, but I thought that completely covering a small surface plate (which Paul has) was easy, the reason why surface plates are damaged by lapping with abrasive paper, is that the abrasive particles get between the paper and the plate, thus lapping the plate. The wet and dry completely covering (taped down) the plate will prevent the abrasive getting in contact with the precision surface.

Offline mm289

  • Jr. Member
  • **
  • Posts: 27
Re: Lapping
« Reply #4 on: January 05, 2018, 09:47:11 AM »
Cheers guys, was the diamond powder just an e-bay purchase Matt?

Thanks,

Paul.

Offline mattinker

  • Hero Member
  • *****
  • Posts: 1107
  • Country: fr
Re: Lapping
« Reply #5 on: January 05, 2018, 09:55:19 AM »
Cheers guys, was the diamond powder just an e-bay purchase Matt?

Thanks,

Paul.

The diamond flour I bought on eBay, It was 45 to 54 Ás which is relatively coarse, I bought it to lap my surface plate. You really don't need much!

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 2114
  • Country: fi
Re: Lapping
« Reply #6 on: January 05, 2018, 12:20:24 PM »
I have done a little of lapping. Pretty much everything else really has failed one way or other but cast iron lapping plate, lapping paste and cast iron/steel has worked fine.

I would use any abrassive (sanding paper) on surface plate only if I had nothing else or nothing else would do.

Glass looks fine, but it is not really flat enenough to metrology. For normal fitting use you need many offcuts, most of them are not that straigh over length of 100 mm. Float glass is always wavy and slanted. Waviness seem to differ from piece to piece. But generally to one direction and 100-200 wave length on 10-12 mm glass I have measured. Also many glasses seem to be slanted, last piece I checked was about 0,1 mm tapered at distance near 400 distance. However, if you use figure of eight and randomize, the part will be more flat than the plate. Only caveat it that the glass ust be suported well ot the part must be light weight. Glass is pretty bendy.

Choosing the abrassive is interesting. I like the diamond when it is rolled into the lap and lap must be accurate like internal lap. Downside of the diamond is that it cuts forever. Loose lap is hard to clean out completely. Silicon carbide paste breaks down and it is very easily available 80/220 grit as a valve laping paste. It wears down fast, which is good and bad. Good thing when it braks dow the same pace as the part gets soother and smoother.

It really pretty much depends how accurate you need to go and are willing to go.

There is actually a learning curve, first thing to learn is that if the part is high and you push it. leading edge will wear down faster. Pretty nice when you try square something and it is just a little slanted. Second thing is to learn how to clean up everything. Third thing to learn is that you need more than one plate...to keep all the plates straight.

I need to straighten one worn granite surface plate. The granite quality is really good but the surface is not straight. Planning to use my lapping plate to straighten new brake rotor disc, check the straighthness of the rotor with another suface plate, then charge rotor with a diamond paste and use it to straighten worn surface plate. Few kinks that I need to verify prior to start.

Pekka

Offline mm289

  • Jr. Member
  • **
  • Posts: 27
Re: Lapping
« Reply #7 on: January 06, 2018, 07:47:12 AM »
In a recent haul of bits I acquired was this massive piece of iron in the pic below, weighs a ton, just wondering if that is a lapping plate.... :scratch:

Cheers,

Paul.

Offline mattinker

  • Hero Member
  • *****
  • Posts: 1107
  • Country: fr
Re: Lapping
« Reply #8 on: January 06, 2018, 07:54:05 AM »
That is a lapping plate!

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 2114
  • Country: fi
Re: Lapping
« Reply #9 on: January 06, 2018, 09:43:47 AM »
Check that it is straight. Three out of three I have tried have more waves than north sea.

How is the other side? Sometimes there is another similar surface, but I have one that has surface plate on the other side and laping plate on the other side - journeyman model.

Pekka

Offline j1312v

  • Jr. Member
  • **
  • Posts: 33
Re: Lapping
« Reply #10 on: January 06, 2018, 12:53:35 PM »
That is a nice haul Paul  :thumbup:,

Specially that small mag-chuck  :drool:

If you don't need the whole plate you can split it in to 2 or 4 smaller plates  :dremel:(depending of what are you looking to lap in the future) and make a set of lapping plates (rougher and finisher or course, medium, semifinish and finisher).

For your surface gauges you only need a nice flat surface and a bit of fine emery. Remember to use white spirits or wd40 as a lubricant and clean the parts after lapping.

Keep up the good work.  :beer:

Bernie