Hints on making Straight Edges out of Steel

[Music] [Applause] no laughing guys hi everyone my name is Alex I'm an engineer and my passion is with design development and prototype production of all sorts of engineering solutions I made this video here because of recurringly your questions about my 1.2 meter or 4 foot long precision straightedge here which I made for the scraping job of my prototype press brake or to be more precise the spotting of the lower girder surface and spotting of the two upper girder surfaces for scraping it a heads up right at the beginning sorry guys I don't have any footage of me actually building this straight edge because when I built it I was pressed for time however in this video I'll walk you through the thought process of coming up with its design and share with you some experiences I had during this build this straightedge is made almost exclusively with basic hand tools because I had no access to such a large surface grinder or even such a large milling machine in order to machine this in one setup for the necessary precision it took me roughly 2 days to make the straightedge however only one surface is scraped why both anyway I think it is fair to say that the straightedge is made against common practice because it's not made out of cast iron but rather it is a weld of design out of three pieces of carbon steel so let's take a look now this implies two bottlenecks which must be solved the first is that carbon steel is a very stubborn material to scrape however this can be overcome to a certain degree by using a dedicated scraping insert geometry like this one and a slightly altered scraping technique I made a video about this particular matter which you can find on my youtube channel the other bottleneck is that the welding must be done in a very careful and thoughtful manner so it's not to compromise the precision and long term characteristic of the straightedge by welding induced residual stresses but before I discussed you with a schoolish monologue let's test the flatness of the straightedge but please note that I made this edge roughly two years ago in a quick and dirty fashion to get my press brake done I didn't use it ever since this one scraping job just had it in store sitting comfortably on this foamy rubber cushion actually this material is for basement insulation construction site stuff but anyway I digress okay guys sorry about the strange view here but I want to show you this test all in one go without a cut in between and as you can see I have my straightedge on my surface plate and the straightedge is longer than my surface plate and what I want you to note is that it is resting on two pins one here and one here in order to give this measurement a defined base now let me sit you down and focus you on the indicator and now let's see about the straightness of this straight edge here but keep in mind that I cannot traverse the whole length of the straight edge I'll try to go as far as I can without cantilevering the base of the indicator too much so let's see now I'm beginning to cantilever again with the base and this is about as far as I can go and this is again as far as I can go so I think based on this test we may conclude that this straightedge is combined design and manufacture are reliable of course two year storage are no real long-term testing basis however two years storage are not negligible either so first a few words about the design of the straightedge generally what we want from a straight edge is rigidity rigidity and more rigidity of the scraped surface I'm sure you're familiar with the straight edges with the rounded back the Camelbak type straight edges a fine and long term proven design no question about that this design on the other hand has two flanges with a filler in between in order to gain more stiffness these flanges here on this particular straightedge they measure 30 by 15 millimeters and yes you've seen right they are out of cold-rolled material with all its potential for residual stress crazy isn't it but you saw the testing result from before still it is surely better long term wise to instead use hot rolled material for the flanges but back in the day I was pressed for time a large overall height generally impacts significantly on rigidity to the power of three that is so twice the height 8 times the bending stiffness overall height here is 200 millimeters the fin let's eat here is 6 millimeter thick and laser-cut however you can also make it by other means flame cutting or conventional machining or even a clever angle grinder excursion if need be I wouldn't use a thinner Filat in this case in order not to compromise the flanges rocking rigidity like so too much the Phillips holes are to reduce weight of the thing keep in mind that the straightedge does deform by its own weight even if only by small amounts also typically you have to handle such a straightedge by hand and this will eventually wear you out it's just a question of repetitions also you have to grab it somewhere for which the holes are nice by the way the holding point should be covered with leather or cloth and when you do the spotting job in order to reduce heat transfer from the hand to the straightedge as much as possible the hole however they should be arranged in a way that the Phillip does not significantly lose shear stiffness which is stiffness against this kind of deformation here so in this case I left these paths here in between the holes which are roughly oriented 45 degree with respect to the straightedge at least of same importance as design is the manufacturing technique before we were talking about the two bottlenecks in making such a straightedge being able to scrape carbon steel is the first the second bottleneck is the welding strategy and the wealth preparation and believe it or not this making the straightedge here does not require a computer-controlled 10x is high vacuum laser welding century instead all that needed is a TIG welder the right strategy in a sensitive hand the welding preparation must ensure that the flanges have a nice surface to sit on here on the Filat particularly this means you must get rid of the bevel on the Filat from for example laser cutting the flange should sit on the fill at faces as perpendicular as possible but on this straight edge here I didn't even machine the fill up faces just finish them with a file and a right angled guide block next we must weld on the flanges you see the straight edge is held together exclusively with tags and this is the main part of the well trade secret if you want for this these recesses here are placed with regular spacing because the recesses corners like here and here are very suitable for fusion tags so basically the recesses serve two purposes firstly they ensure it defined tag spacing and secondly they allow for small well-defined and strong texts at corners at these points here this one this one and the next one where the 45-degree paths and shear stresses are transferred in the flanges and here I use text at each corner here two and two on the backside to also give the flange some rocking stiffness against deformation like so in between the 45 degree paths i tacked in two places here and here in the Phillips Center generally the tacking sequence I used here is from the center towards the ends kind of like placing a sticker on a painted surface and pushing out the air bubbles and I alternated top and bottom flange tacking that is taking two spots here then two spots here and so on well and finally we have to scrape the straight edge of course to give it its precision in this video I don't show the actual scraping work however you can find hints on this matter with carbon steel in my already mentioned video but I want to discuss briefly a few things about spotting such a straight edge typically this would be done on a surface plate like here in this setup but you do not absolutely need a surface plate instead you could also tackle the spotting issue by making three identical straight edges and spot them with each other in a smart alternating manner the theory of this is called the three plates method in case you want to look it up so job could be done by a tenacious guy even in the field with minimal equipment whatever kind of scenario this would require I don't know but still it's a little tricky to scrape a straightedge like this one which is comparatively narrow in relation to the height because there is a big danger of the straightedge starting to leave more and more to one side as you go from scraping cycle to scraping cycle and in order to avoid this what I do is I use my right angle master block here and use it as a back rest during spotting and then I wrap the straightedge against the surface plate like so and this should ensure that you do not drift toward one side or the other side from scraping cycle to scraping cycle and finally a side note on this particular straightedge here you see I cannot completely spot this one on my surface plate not even diagonally generally this is a problem but if the overhang here is not too large you can still succeed with scraping such a straight edge flat if you interpret the spotting pattern right you see due to the overhang the spotting pattern will get more dense in this area of the straightedge then it is here even for a perfectly flat straight edge so what you have to do during striping is not to follow that temptation to straight away more material here than here generally what's good practice if you have overhang is to flip the straightedge around on the surface plate after each scraping it's boring cycle so as to compensate for the error one makes by misinterpreting the spotting pattern but now enough about these details because you may not be suffering from overhang at all alright guys I hope these little secrets of the trade are helpful for you in some kind way as always thank you very much for your interest in this video I appreciate your time all the best for your scraping projects and thank you [Music]

Channel: An Engineer's Findings

Views: 11,905

Rating: 4.9897828 out of 5

Keywords: straight edge, scraping, surface plate, spotting, precision testing

Id: YanlyahWDOw

Length: 14min 39sec (879 seconds)

Published: Sat Apr 25 2020