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Lapping (and honing) - some techniques for discussion

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Ramon Wilson:
Hi everyone.

We all know this subject has been prominent of late and this new thread will hopefully cover it in depth.  I have posted it under this banner for no reason other than it doesn't seem to fit anywhere else - perhaps there should be a new heading - Workshop Techniques? If it's felt it should be moved elsewhere however please do

Rod - 'Tangler' and Jo have specifically asked if the method used could be described and several others have endorsed that. Before we get going I would like to stress that this is very much how I carry this out and definitely not to imply that it is the way.
Any comment, constructive or not is welcome - the actual process is basic but the manner in which some approach the manufacture of laps does differ. I have a pretty fixed way of going about it as quite simply 'it works'. Not technically trained in the process the skill and experience has been acquired however by carrying it out on occasion over a number of years and particularly so on these small diesels.

Based on what's been done over the years hopefully there will be plenty of images to convey the process but that said  it's not going to be dealt with in one post  :o so bear with it  ::)

Okay then - who was it said 'start at the beginning and go on to the end'.

After the Linley mill was acquired it was not long before it became apparent that the means to sharpen cutters would be required. Just about this time the Quorn appeared in ME and so I set out to build one. At that time I had had no formal machining training and had only been model engineering for a short few years. I was however in a club and said club had a member  - one Len Evans. You may perhaps recall I have made reference to him before  ::)

I discussed with him what I saw was a major problem namely the means of getting four bores the exact fit for the lower bars on the Quorn. Len's answer was immediate - bore them. But I lacked the confidence to guarantee the size. " In that case you need a lap" and so began my experience with lapping. Following his instructions I bored the holes to within 2 or 3 thou (I was 'imperial' at that time ;)) and made my first lap which I still have, unused since those first four 1" bores....


The lap material is copper wrapped around a steel mandrel that is cut away like a D Bit. The copper is silver soldered to the leading edge of the 'D' and the cut away portion is inserted to enable expansion via a grub screw. Once soldered it was held in the lathe and turned to about 1-2 thou down on the bore size - the anular gap so created being neccessary to contain the lapping compound. If I remember correctly and it is a long time ago valve grinding paste was used  - I can't remember much else except that it was not difficult to do - the lap removed the metal far quicker than anticipated and the finish and size of the bores were far better than hoped for. Those first tentative steps had proved successful and a new skill had been acquired albeit one that would be some years before being put into use again.

Though it's thought that the design was one described by Len Mason it's not certain where the the method of making this type of lap was acquired from - there's no claim for originality that's for sure but many similar laps have been made over the years since that first one and all have proved extremely successful and easy to use. Despite the fact that they don't open radially they retain their circularity even after considerable use though they do tend to become a little eccentric to the shaft but as this process is all carried out as a floating operation that does not appear to have any detrimental effect.

These are some of the laps made in the same fashion since that time all, except that first one for the Quorn, made for model engine cylinder bores. The actual method of manufacture will get covered later.


The larger one to the left was made for these....the liners and cylinder barrels for the Bentley BR2.
 

Neccessary to overcome a big oversight on my part :o that will have to wait until tomorrow I'm afraid - it's been a long day and I'm feeling quite whacked  :old:

Regards for now - Ramon

ths:
Thanks for that ,Ramon. Your laps look so much more long lasting than the ones I have made before, an external one for the GHT sensitive drill quill, and an internal one for ETW's Argus oscillator! The latter was done, I'm sure, just to do it. The internal hone was done to a Len Mason design that can be found in 'Using the Small Lathe'. They both worked extremely well, I used valve grinding paste, coarse and fine, and a few scratches remain on the quill from the use of the coarse. I have since acquired a set of diamond grinding pastes in syringes, but have yet to use them.

Looking forward to more of this strangely satisfying topic!

Cheers, Hugh.

Don1966:
Ramon, you have my full attention. I know you showed these once before, but I am glued to more of you teaching. I await your making of the lap and demo of its use. Thanks much for taking the time to demo them for us, much appreciated.

Don

b.lindsey:
Nice start on this topic Ramon...folowing along with interest however long it takes.

Bill

steamer:
Oh you can count on me taking copious notes!

 :praise2: :praise2: :praise2: :praise2: :praise2:

Dave

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