One has to be careful of expertise found on the internet. Anyone can post something plausible and assert it to be the final word in a particular topic. Without knowledgeable technical editing, peer review, and in the absence of critical comment, there's no way for the naife to assess the material for technical merit. If he accepts the material at face value, he can make a significant investment in time and or money pursuing flawed expertise and may come to naught for all his time and trouble. What does he do then?
I looked at the material Mr Swenson posted and from my experience (I rebuilt machine tools for a living for two years and maintained the scraped references used in the process) I submit his stuff is better than most. Its faults lie in its ommissions.
Mr Swenson casually brings in one of the masterpieces of precision technology (Moore's "Foundations of Mechanical Accuracy") tacitly suggesting his techniques in accordance with it when in fact the techniques he promotes are but roughly adapted and the results you can expect are 1/20th the accuracy routinely addressed by Mr Moore.
The images Mr Swenson uses to illustrate the working together of three edged to acheive straightness are well done as far as he went. The process Mr Swenson attempts to convey is better explained in Porter's "Engineering Reminiscences" Chapter XXI and of course the relevant chapters of Connelley's "Reconditioning Machine Tools."
Swenson states his process is best suited for linear straight edges suited for checking the tables of woodworking equipment rather than as a scraping reference for machine tools where the accuracy required is a full order of magnutude higher. I agree.
He fails to mention temperature and the effect of physically handling precision apparatus and the use of cleaning solvents (alcohol) having a high heat of evaporation.
Neither does he address how to deal with the indications the uses of transfer media (Prussian blue and similar colors in oil) brings forth.
He slips by discussing how to "remove material" in detail (filing and stoning instantly come to mind) by merely alluding to it. This is highly skilled work and a few paragraphs devoted to "material removal" in some detail would be a welcome addition to the naive reader.
His omission of the importance of cleanliness where lapping is concerned is particularly telling.
So, Bioman, if you desire to make a straighedge suited for woodworking and you're capable of dedicating considerable time, you have good hand filing skills, your native wit leads you to avoiding the pitfalls of unequalized temperatures Mr Swenson's discussion may lead you to making some very serviceable straight edges.
If you desire to make a camel back straight edge or a fitter's flat for precision scraping, then Micheal Moore's booklet and goods are a better choise than Mr Swenson's.
Remember that precision references like straightedges are dependent on the stability of their materials. Second class materials like black structural steel poses significant disadvantages not the least of which is its softness and ready deformability.
[ 08-17-2005, 02:39 PM: Message edited by: Forrest Addy ]