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  • Making Dovetail Straight Edges

    First off, this aint a how-to, unless you want to learn how to do everything the wrong way! This is just my chronicling my first attempt at it!

    Decided i needed a few dovetail straight-edges around the shop for a few projects down the road, as some point im planning on doing a complete tear-down on both my mini mill and lathe, all the little odds and ends. New bearings, delrin feed nuts, and most importantly, scraping the ways in so the movement on the table/cross slide is actually smooth. My opinion is that both the machines could work pretty well for the kind of work that i do, but 90% of the problems could be improved with better fit and finish of the moving parts.

    So, making a few straight edges serves a few purposes. The first is, well, i need a straight edge so reference the dovetails off of. The second, and arguably more important reason, is scraping is a bit of a new skill for me, and id rather not learn on my tools. Much cheaper to kill a piece of cast iron after all. I figure, scrap in 2 or 5 straight edges to get a feel for it, get the process down, then move on to the expensive stuff.

    Started off sourcing some cast iron, which turned out to be quite the task. Nowhere local to me carried it, somehow, and very few places online seemed to carry it. Fortunately, one of the forum members here came through in a big way, so i got a pretty massive piece of dura-bar to work with. Started off by hacking off a few pieces of roughly the right size. Funnily enough, hacking off a few pieces ended up being the hardest part, so far. My cheapie little portaband didnt want to cut without the blade wandering, so my pieces came out pretty wonky. Nothing that didnt mill off, milling just took a bit of time:


    Up top is a rough cut piece off the saw, down below is a piece ive already taken down to dimensions of about 1x3/4x9ish. Really i wasnt going for any exact dimension, just wanted to get it as square and flat as i could. Thanks to the wandering of my bandsaw blade though, i had to cut the pieces close to 3/8" oversize, so i ended up with a fair bit of material to hog off with my little mini-mill. A 2 inch carbide face mill did a pretty fair job of it, though it did take a bit of time, the iron milled pretty nicely but i was still limited to about .030" DOC before the mill started making some pretty funny noises.

    Cutting the angle for the dovetail proved to be a bit of a challenge. I had originally assumed i would need something along the lines of a sine vise, but in a post here i made a while back a few people made the very valid point that there was no reason that the straight edge angle needed to be exactly 60 degrees, in fact it needed to be less and wasnt critical. It still took some doing, figuring out how to cut the angle, but i managed to work something out that worked with my present tools. I ended up cutting a few wedges of ~55 or so degrees from some aluminium, then superglued them to the cast iron so i could grip the bars in my vise at the proper(ish) angle:


    Youll have to excuse the glare in the photo, it was kinda hard to snap. The setup was a little dicey, but it ended up working better than logic and reason say it shouldve. It did make me realise i need to invest a little in better workholding setups, a sine vise wouldve been really nice to have, even if it wasnt really needed, and some machinist jacks have made their way onto my wishlist. I ended up having to improvise a way to support the right side of the stock with a few 1-2-3 blocks and a bolt. Somehow it worked, and i got a pretty nice looking and fairly flat surface, but it really falls under "redneck engineering" and its not a setup id like to repeat.

    Anyway, heres where the straight-edge blanks sit now:


    I ended up maging the 2 different sizes, one is 3/4"x1", the other 1/2"x3/4". Bandsaw blade wandered a bit more than i though when i was roughing the blanks, but it ended up being for the better. The smaller one seems like itll be a little easier to maneuver. Now im just waiting for the Hi-Spot blue i ordered in to arrive before i can start the actual scraping. As it turns out nowhere local to me carries it. In the meantime though, i think I might start by 'lapping' the blanks with a piece of sandpaper, my mill didnt make a perfectly flat surface and im thinking starting with the surface a little closer to flat will make the scraping go by quicker.

    Ill update once i can actually start working on these a bit more. In the meantime, id more than welcome any advise anybody cares to lend!

  • #2
    Excellent work. Can you post a photo of an end view of those?

    Dan L
    Salem, Oregon

    Comment


    • #3
      If you want an angle reference, the best idea is to make a short one that is not a lot of trouble to make. a couple inches is as much as you will need.

      As for the dovetails themselves, it is really not critical what angle they are at exactly. Close to nominal angle will help if you ever need to replace the slide.

      You can simply scrape the longest dovetailed part of the system (usually the slideway) to correct geometry, as far as flatness, direction, and distance between, etc. Then the shorter part (saddle or slide, usually) can be scraped to match more easily. (if you scraped the slide dovetail first, you would need to scrape the whole long slideway to match the slide).

      I usually scrape the flat bottom of the slide to a granite flat (so that the two sections match) , then use that part to align the two surfaces on the slideway so they are in one plane. Then the dovetails on the slideway, for flatness, parallel, and alignment to external parts. Finally the dovetails on the slide are scraped to the dovetails on the slideway. Often with lesser equipment, one of the slide dovetails will have a gib of the multiple screw type (not tapered), so that side of the slide does not require scraping at all.
      1601

      Keep eye on ball.
      Hashim Khan

      Comment


      • #4
        Originally posted by Danl View Post
        Excellent work. Can you post a photo of an end view of those?

        Dan L
        Can do, it'll just have to be later tonight. Dunno why I didn't have one to begin with, should've occurred to me that would be nice to have
        Originally posted by J Tiers View Post
        If you want an angle reference, the best idea is to make a short one that is not a lot of trouble to make. a couple inches is as much as you will need.

        As for the dovetails themselves, it is really not critical what angle they are at exactly. Close to nominal angle will help if you ever need to replace the slide.

        You can simply scrape the longest dovetailed part of the system (usually the slideway) to correct geometry, as far as flatness, direction, and distance between, etc. Then the shorter part (saddle or slide, usually) can be scraped to match more easily. (if you scraped the slide dovetail first, you would need to scrape the whole long slideway to match the slide).

        I usually scrape the flat bottom of the slide to a granite flat (so that the two sections match) , then use that part to align the two surfaces on the slideway so they are in one plane. Then the dovetails on the slideway, for flatness, parallel, and alignment to external parts. Finally the dovetails on the slide are scraped to the dovetails on the slideway. Often with lesser equipment, one of the slide dovetails will have a gib of the multiple screw type (not tapered), so that side of the slide does not require scraping at all.
        Thanks for the tips on order of operations. I haven't come up with an exact plan of attack yet, I'm still trying to sponge up all the information I can. So far the 2 links below have been my Bible for this, both are for mini Mills rather than lathes, but the concept is about the same. Planning on doing the mill anyways, so it sure doesn't hurt to plan

        http://www.modelenginemaker.com/inde...306.0/all.html
        http://www.cnczone.com/forums/bencht...57385-cnc.html

        Comment


        • #5


          And a quick end-on shot. Hi-Spot should be hear tomorrow according to UPS, so i should be able to get to scraping!

          Comment


          • #6
            Might be a bit soon after cutting, I've found stuff cut long and slim moves about a bit as the stress settles down, I was told that sticking in the oven at a low heat helps, I can see the logic but haven't tried it.
            Otherwise good job, hand held bandsaws tend to be a bit challenging, sometimes I've cut curved once and every time I used it after it wanted to cut the same, the set must have been buggered
            Mark

            Comment


            • #7
              Originally posted by boslab View Post
              Might be a bit soon after cutting, I've found stuff cut long and slim moves about a bit as the stress settles down, I was told that sticking in the oven at a low heat helps, I can see the logic but haven't tried it.
              I don't think its a bad thing to do, but its advantages seem an unresolved subject imo. Laslo who used to post a lot here claims latest engineering info suggests it is (or sited a reference that claims) an old wives tale that cast iron creeps. Offsetting that are armies of apprentices and machinists who hot cold cycled parts to work out the stresses. Of course we know the tales of manufacturers burying castings to remove stress - removing stresses is definitely a real thing to achieve stability for subsequent ops, but the need to do so after after all cutting and work is done is according to one source, disputed.

              I'm not sure which is right. but I find the idea compelling that if you finished up cutting a piece its not going change shape (plastic deformation) on its own....except for this thing called creep. But apparently creep only happens with lots of force (but less than that required for plastic deformation) The other belief is that ringing it for awhile with a hammer removes stresses. Could be, but whether those stresses will change shape or not is not clear.

              It can't hurt, but in my experience a good piece of cast has shown to be quite stable.
              Last edited by Mcgyver; 11-27-2017, 11:54 AM.
              in Toronto Ontario - where are you?

              Comment


              • #8
                Originally posted by epicfail48 View Post
                Funnily enough, hacking off a few pieces ended up being the hardest part, so far. My cheapie little portaband didnt want to cut without the blade wandering, so my pieces came out pretty wonky.

                ... Thanks to the wandering of my bandsaw blade though, I had to cut the pieces close to 3/8" oversize, so i ended up with a fair bit of material to hog off with my little mini-mill.
                Until a purpose-made horizontal or vertical bandsaw enters the picture, have you considered creating a bench w/ a table your portaband can be mounted to in a way that it functions as a vertical bandsaw? There are several links and videos with examples of how others have gone this route.

                If you have access to a welder, fast-forward through this video to see the end result: M^3 Portable Bandsaw Table Build

                Below are a few commercially available products for additional inspiration


                A feature I do not recall seeing on portable band saws like my Milwaukee is an extendable blade guide for the purpose of closing down the unsupported length of blade across the throat gap to the minimum necessary for the material to be cut - like on purpose-built saws. If you incorporated something like this in your modifications, it would help further improve cut accuracy.

                Originally posted by epicfail48
                You'll have to excuse the glare in the photo, it was kinda hard to snap.
                Consider buying or building a tripod or other mount that will stabilize the camera/phone well enough to permit long exposures and higher f-stops in ambiant light for well-lit, sharp images with good depth of field.

                Frank Ford's site shows a camera-mount rig he built for his shop that can be easily moved from place to place around the work area. Compose the scene, set the timer and voila! - great pics.

                One or two inexpensive flex lights on mag bases fitted with warm white LED bulbs from CREE (CREE features good Color Rendition Index numbers) will be a benefit. Use these and cover up the window.
                Last edited by EddyCurr; 11-27-2017, 01:27 PM.

                Comment


                • #9
                  Good job but beware that those straight edges will likely bend over time. I made just the same thing and it printed in nicely. Six months later it would spin like a top and I had to scrape a couple of tenths off the middle to get it to print again.
                  Peter - novice home machinist, modern motorcycle enthusiast.

                  Denford Viceroy 280 Synchro (11 x 24)
                  Herbert 0V adapted to R8 by 'Sir John'.
                  Monarch 10EE 1942

                  Comment


                  • #10
                    I'm most of the way through making a similar straight edge 14" long out of Durabar. The bar was cut a little over 4 years ago then milled off about 3/16" on all 4 sides. I let it sit for about 6 months then checked it. It had moved about .003" out of straight. So,not having any way to stress relief anneal the thing, I just put it in the oven at 500*F for an hour then let it cool overnight. I repeated that cycle four times, then cut it straight. A few months later it hadn't moved! So I machined the 60* angle and it still didn't move. Cue the scraping action.

                    That's where I am now; it's within about two tenths overall with good print on all sides. If I apply my self another few hours of work should finish it.

                    Then I can get on with straightening my Benchmaster mill!!

                    Persevere!!

                    Pete
                    1973 SB 10K .
                    BenchMaster mill.

                    Comment


                    • #11
                      Originally posted by boslab View Post
                      Might be a bit soon after cutting, I've found stuff cut long and slim moves about a bit as the stress settles down, I was told that sticking in the oven at a low heat helps, I can see the logic but haven't tried it.
                      Otherwise good job, hand held bandsaws tend to be a bit challenging, sometimes I've cut curved once and every time I used it after it wanted to cut the same, the set must have been buggered
                      Mark


                      Originally posted by Peter. View Post
                      Good job but beware that those straight edges will likely bend over time. I made just the same thing and it printed in nicely. Six months later it would spin like a top and I had to scrape a couple of tenths off the middle to get it to print again.
                      Originally posted by 10KPete View Post
                      I'm most of the way through making a similar straight edge 14" long out of Durabar. The bar was cut a little over 4 years ago then milled off about 3/16" on all 4 sides. I let it sit for about 6 months then checked it. It had moved about .003" out of straight. So,not having any way to stress relief anneal the thing, I just put it in the oven at 500*F for an hour then let it cool overnight. I repeated that cycle four times, then cut it straight. A few months later it hadn't moved! So I machined the 60* angle and it still didn't move. Cue the scraping action.

                      That's where I am now; it's within about two tenths overall with good print on all sides. If I apply my self another few hours of work should finish it.

                      Then I can get on with straightening my Benchmaster mill!!

                      Persevere!!

                      Pete
                      I know it's a bit soon after the rough milling, and I'm expecting to see a little movement in these down the line. The way I see it though, is it either ends up as more scraping practice, or I get pleasantly surprised 6 months from now when they haven't moved. Before being used on anything critical I was already planning on spotting them, just o double check straightness

                      Originally posted by EddyCurr View Post
                      Until a purpose-made horizontal or vertical bandsaw enters the picture, have you considered creating a bench w/ a table your portaband can be mounted to in a way that it functions as a vertical bandsaw? There are several links and videos with examples of how others have gone this route.

                      If you have access to a welder, fast-forward through this video to see the end result: M^3 Portable Bandsaw Table Build

                      Below are a few commercially available products for additional inspiration


                      A feature I do not recall seeing on portable band saws like my Milwaukee is an extendable blade guide for the purpose of closing down the unsupported length of blade across the throat gap to the minimum necessary for the material to be cut - like on purpose-built saws. If you incorporated something like this in your modifications, it would help further improve cut accuracy.

                      Consider buying or building a tripod or other mount that will stabilize the camera/phone well enough to permit long exposures and higher f-stops in ambiant light for well-lit, sharp images with good depth of field.

                      Frank Ford's site shows a camera-mount rig he built for his shop that can be easily moved from place to place around the work area. Compose the scene, set the timer and voila! - great pics.

                      One or two inexpensive flex lights on mag bases fitted with warm white LED bulbs from CREE (CREE features good Color Rendition Index numbers) will be a benefit. Use these and cover up the window.
                      Some form of table for using my bandsaw horizontally would certainly be nice for most of the work I do, but in this particular instance wouldve been akin to tilting at windmills. I was using a high-tooth blade with some age to it to go through 2 inches of cast iron, on a saw that barely tracks the blade to begin with. Pretty perfect storm for blade deflection, though I'll admit I wasn't expecting nearly 1/4" of deflection. Think I'll try an angle grinder too.

                      I've also got a pretty good photography setup, just didn't seem worth setting it all up to take a few snaps of a metal bar. I'll save that for the end when they're all shiny and scraped in!

                      Comment


                      • #12
                        I missed the part about the high tooth count earlier.

                        Originally posted by epicfail48 View Post
                        I've also got a pretty good photography setup, just didn't seem worth setting it all up to take a few snaps of a metal bar. I'll save that for the end when they're all shiny and scraped in!
                        The beauty of Mr Ford's rig is that once implemented, there is little to set up - it is just THERE, pretty much ready to use for project documentation whenever the desire occurs. A foundation for consistently great photos w/ minimal impact on momentum.

                        In case you haven't already seen:

                        Comment


                        • #13
                          Alright, the Hi-Spot came in today, so i actually managed to get some work done, and i gotta say, its going better than i thought it was going to. Started off by using a strip of sandpaper to roughly lap the straight edges a little closer to truly flat:


                          You can see that theyre pretty shiny in the center, whereas the ends still have some pretty clear tool marks. Seems to be a pretty clear indication that my mill had some trouble with table sag at the far ends of its travel. Thats one of the biggest motivators for this whole series of projects, i dont like the fact that i have to tighten the gibs to the point where i can barely move the table and i still have dimension issues like this. Anyway, after the lapping, i went ahead and printed (pretty sure thats the right term) the parts:


                          Took a few tries to get the thickness of the dye right. First time i applied it way too heavy to the plate, wiped it off and tried again and it was way too thin for the roughing passes. Once i got that figured out everything went pretty smoothly, the dyechem stuff was easy to see where it was spotting, and the cast iron was almost entertaining to scrap. Print, scrape, clean, repeat. The first printing showed more of what i already knew, that the center was high by a decent bit. After 35 iterations, i ended up here:


                          Spots all along the length of the straight edge, though the density of the spots is hardly where it needs to. I was ling on the dye fairly thick for these few rouging iterations, just to get the process going a touch faster. Ill start thinning out the blue as i get closer to the end. I went ahead and stopped there for the night, ill consider that plenty roughed in and will spend the next few days bringing up the precision to where it should be.

                          Course, the problem there i where the precision should be, ive heard numbers anywhere from 30 to 55ppi for a reference edge. Anybody care to weigh in? I was thinking 35-40 would be a good target for me. I understand that more precision never hurts, but i feel like in my case id hit a point of diminishing returns, where the added effort for the extra precision would outweigh the actual benefit for me. After all, these are being made with a grade B surface plate as a master by a complete amateur and will be used to scrape in the ways of what is generally considered to be a Fischer Price mini mill. Seems like it would be a touch of overkill to go for laboratory grade AA for that

                          Comment


                          • #14
                            35 - 40 ppi should be plenty good. As you break up the high areas you have now the greater points per inch should come in fairly quickly. There are no big holes of non contact and the areas showing no ink at the moment are probably not far below the contacting surfaces.
                            .
                            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                            Comment


                            • #15
                              Originally posted by TGTool View Post
                              35 - 40 ppi should be plenty good. As you break up the high areas you have now the greater points per inch should come in fairly quickly. There are no big holes of non contact and the areas showing no ink at the moment are probably not far below the contacting surfaces.
                              Well that's certainly reassuring to hear, that it should take horribly long to get the point down. Getting to this point didn't take too much time, about 2 hours, but still, I couldn't really feel my arm at the end! Not hard work, but a little repetitive

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