Machining a Miniature Engine Lathe - Part 6a - Cross Slide Dovetail Prep

hey guys joe pie here at advanced innovations welcome back to the shop the next step i'm going to take on a little mini lathe project is to cut the dovetails on the crust slide and the well all the cross side dovetail features now there's a couple of different ways you can measure dovetails and i'm going to show you two ways that i know of one of them is just it just seems so obvious it's not even funny and when you see the math you'll see the way it falls out you're gonna just it's it's almost too too good to be true so i'm going to show you the first way the conventional way with pins both ways are with pins but pins of different sizes so that's being said let's take a look at the feature the way the feature is going to be cut on that little project i am not a big fan of over constraining a dovetail i don't need it to hit on the bottom on the 60 degree and on the top two of the three are fine you don't need all three you just don't chances are you grab a six inch scale out of your apron you can slide it underneath the cross slide because it doesn't touch touches on the sides touches on the bottom that's what we're going to focus on here therefore the bottom inner corner is the gauge point that's the point that i want this can be as deep as you want it to be but this is the corner that has to make as the thing goes together my feature is going to be 130 deep 60 degree dovetail now looking at this particular graphic you're only looking at one side of the female cut this is the part of the tool post that slides back and forth compound two pins one on either side gauge block in the center that's how you measure it you do all your math you come up with the point to point dimension and all is well how do you find it well let's start doing some geometry here unfortunately dovetails you're going to have to do some trig you're going to have to do some geometry but a 30 degree or 60 degree dovetail in my opinion is one of the easier ones so let's look at the pin where are the triangles here actually there's one right here 130 60 degree let's put that down here maybe you'll be able to see it 130 base 60 degree up top right there triangle a let's call it and that's just you can come back and freeze frame and stare at it and scratch your head and go i don't know what he said next geometric construction rule i'm going to use nice straight edge to do this i'm going to draw a perpendicular line from the top and i'm going to draw a perpendicular line from the side because as far as construction goes in geometry the tangent point of any circle coming up against the corner is a right angle and we're going to talk right there since that's a right angle and that's a right angle and this side equals that side because these are the radius two sides the same bisected angle this is a 30 degree this is also a 30 degree these triangles are the same it's right there radius of the pin let's not even consider the radius of the pin yet it will come into play looking at this triangle here if you were to flip this line parallel over to here you'd have exactly the same triangle forming a large rectangle so this distance right here will be translated to up here okay can you see it slide it over these two numbers right here one inch 1547 and 0.86603 are the two most important numbers if you're going to be working with hexes with 30 60 90 triangles right there lock them in your memory banks write them on your hand stick them in your toolbox whatever right there i am not going to use trick tables because i have standards i am going to use a calculator to proceed so let's see how fast all these numbers are going to fall out of this let's call this just for sake of being smaller than the depth of the dovetail the pin diameter i don't know pick it 100 000 let's call it 120 just so it's not a bunch of zeros diameter 120. which makes r 60. all right 30 degrees on any 30 60 90 triangle which is exactly what you have here the hypotenuse is twice as long as the smaller leg so this leg right here alone is 120 right there 120. the base leg is 120 times 0.86603 let's see how that works out let's call it 104. it's actually 103.9 for everybody that's going to be splitting hairs but close enough 103.9 call it 104. all right super important you now have 104 right there now what we want to know before we can start using this pin is how far is it from the center to this point or from the edge tangent of that pin to that point because really you don't have anything here that's incredibly useful right now let's use the same exact math that we just used on this triangle here as a matter of fact i'm going to block that out so you can see it there you go the 130 multiplied times this one right here will give us the diagonal leg 150. 150 and a tenth it's not even worth arguing about same thing and that's his trial down here knowing that the half the hypotenuse 0.75 right here now you got all kinds of good stuff you can use 104 minus the 0.75 because they're starting from the same place where's the difference center line's dropping down there's our dimension we want right there 0.104 minus 0.075 29. there is a 29 thousandths difference between the center point of the 120 pin in the corner right there the radius oh 60. gives you your number from here to here which is the gauge point here so basically o29 times two because you've got this gap on both sides of the dovetail plus one diameter radius times two whatever that stacks up at subtract that number from your required point to point and that will be your block size there's a lot to think about right there we roll it back watch it a couple times it will make a lot of sense two triangles you find out two triangles you have a difference in the two triangles plus the radius now you have things you can work with gives you your block size not all that bad now the ideal scenario and i was just working on this a little while ago the ideal scenario would be to put a pin in here that you don't have to do all this but what size is that pin you can just try all day guessing back and forth right we want to put a pin in here where the center that pin is right over that point right there how do you do it it's a lot easier than you think i couldn't believe it when i finally worked it out and it might be well known but maybe not who knows let's check it out let's wipe this off here so you can't see it anymore so all right so now you have exactly the same geometry on the outside 130 deep oh 75 150 leg 60 degrees all is well we want to know what size pin fits in there that the pin is right on that dot right there you are not going to believe how easy this is same tribe triangle a by knowing it's 0.75 on the bottom it's all 75 on the top bisect the angle 30 degrees 30 degrees now we're working with the same 30-60-90 triangle that we've been working with now watch this this is just going to floor you when you shoot that corner angle out it's going to bisect the vertical in one specific spot well guess what you got 30 degrees on both sides you've got a common hypotenuse on both sides therefore this leg equals this leg right there go back to the rule of construction with the geometry with the tangent point of around forming its right angle you now have the center point of your pin right there it just it just fell out so with one triangle you can find the radius of the ideal pin to put the center over that edge right there let's do the math 0.75 times 1 inch 1547 oh 86 6. oh 86 6 the vertical half the hypotenuse this is o433 and so is this now here's the cool part that's the radius of the pin so you double that to find the radius of the pin it's like oh wait a minute i don't even have to double that because it's right here as soon as you figure out that top triangle and find the hypotenuse from the vertical gauge point it gives you the diameter of the pen that is just too easy the thing that's not easy is you're not going to go to your toolbox or your inspection area and find two identical o86 six diameter pins so it's nice to know the first method and come up with that little gap correction and go that way but i had to show you that there's your first triangle same as this triangle right here use that as the base leg use these numbers to have everything fall out and it gives you the diameter of the ideal pin knowing that you have your gauge block dimension plus one diameter there's no corrections there's no secondary triangles to be had there it is i will double check this both ways when i do my dovetails but i have to show you that first let's go out cut some dovetails okay just to prove a point from what i just said on the board yup look at that scale slides right under what does that tell you that tells you that the depth of the female feature is deeper than the height of the male feature that's exactly what i intend to do so if you're going to drive a dovetail i'm not a big fan of driving it from that corner right there i would rather drive it from that corner down there because these two surfaces here and underneath common of course are the working surfaces for that dovetail driven exclusively by the numbers on the print you can see how they've got this dovetail dimensioned at the top corner well if this gets deeper and you continue to hit this 500 this bottom closes up trust me it will so by using the numbers on the print 500 across the top 125 triangle right here do the math back out the numbers that you need to back out to come up with the across the points in the bottom right there now once you have across the points in the bottom you can make this 125 whatever you want when you do beware that it's going to get a little thinner on the walls make sure you have enough meat to do that i'm going 5 000 steeper on this particular feature and i will on the height of this feature here and they have 125 and 500 so this thing would be squeaky tight i'm making mine 130 deep that's my personal preference and before i go and i put these actual parts in there because that's the actual top of the cross slide and that is the cross light itself i'm gonna cheat i'm gonna set up i'm gonna use some blanks just to prove the numbers work no shame in a setup piece guys none let's do it first step in the process is to deck the top of this blank off and cut a channel down the center of it to the finished depth of the dovetail finish depth is 130 i may go to 129 and clean the bottom up with the dovetail cutter check the cutter you're using make sure it is a bottom cutting cutter which most of them i would say are let's do this 355 wide i'm shooting for on this slot 130 deep technically i just formed the bottom corners of the dovetail but if you gauge this correctly with the pins as we're about to do you can make this wider and all it will do is result in a break edge on the sharp corners that would normally form 60 degree dovetail cutter is loaded and offsetting your features like this this 5000 gap that i've put in there is probably going to help if there's any broken corners on your dovetail cutter you can also use a 45 degree chamfer tool on the male section to avoid any interference problems in the corners i'm gonna put a little bit of black sharpie marker down inside the channel bring the cutter in and just scuff it and then we'll work the channel back and forth to achieve the gauge dimension with the pins at least that's the plan let's see what happens we have a nice crispy dovetail cut in that i'm gonna put the two i'm using a 126 diameter pin because i had two of those that matched and that makes the center 166 8. we'll sneak up on that and see if we can get that to work out [Music] i have two different size pins here one's a 164 and the other is a 167 knowing that the 164 does not go tells me i have at least three more to go if you want to use an even number like a 163 pin that would give you a fourth owl leeway when it doesn't go so you can make your adjustments equal distance adjustments the same amount so i'm going to take another 2 off of both sides and see what happens since the 164 doesn't go if i add another four chances are 168 is not going to go let's see if that's true 164 just sneaks in there that's beautiful i like it all right looking for 167 if 164 goes i have another thou and a half to go which means 13 and a half each way final answer all went well that should be a nearly gauge perfect slot right there 126 pin on each side you want to mess with a co-worker doing this sometime change out one of the diameters of the pins when he goes get a cup of coffee he'd come back engage it and watch his watch his color drain from his face that's just mean so don't do that read about that in the book somewhere all right 164 falls in there 167 should just about stand all by itself which it does i like it i'm gonna leave well enough alone set up piece i'll take it i got my number so i have my cutter if there are any burrs or anything on this part while it's set up now would be the time to knock them off put another block in there make the male part and we'll put them together turns out that cutting and measuring and external dovetail is a whole lot easier than doing the internal considerably less math i'll take you back inside and show you that on the board in a minute let's cut this one to 125 tall and let's go for about a thou clearance on the other part i just made i will use the other part as a gauge knowing the diameter of the cutter is important to do something like this because that's what you're working with right now the radius is from the diameter of the cutter and for all you guys with really good eyes yep i need to deck a little bit more off the top of that part you're absolutely right looking for about 700 over these pins and if there's anything less i will be greatly disappointed but i don't think it will be let's see what we get it's gonna be about 20 over 10 over four and a half more both sides [Music] boy there's no movement in that nice i like it there is literally no movement in these blocks you crank this thing back and forth a few times the aluminum would transfer it with cold weld and you say well okay i don't know what happened there but super tight is not always good but that is exactly what i'm looking for that is just absolutely beautiful nothing moving there literally nothing moving you can see the five thousand gap between the top of the male part and the bottom one and just for sake of keeping everybody content i'm going to take a file and i'm going to break this corner off right here if there is a radius inside here it is very possible that they're hitting so just by knocking that corner off this thick could get a whole lot easier i'm not getting myself all full of this nastiness i'm going lengthwise with the edge so i'm not rolling a burr over either direction i'm using a file with no teeth on the edge so i can rest it down on the part itself and not do too much damage let's see if that unloosened it a little bit oh yeah it sure did look at that still an outstanding working fit okay now i have my numbers for both ways and that little experiment right there tells me that i do have a break edge on this cutter not anything too horrible but it's there all right pop it out get a closer look now we got the numbers to do the real part with minimal deburring off camera there is the final result you can see how the 130 on the top piece on the depth doesn't affect anything at all i fit on these [Music] that's beautiful very pleased with that let's take a quick trip back to the white board and i will show you the math behind successfully cutting the male it is so much easier than the female i'm not even going to touch that line with a 10 foot pole all right let's go back on the board for a second show you the numbers behind that real easy let's take a look at the mechanics for an external or a male dovetail feature this is one side of the plateau okay 10. i used the 126 pin to do the part that i just had the height does not matter at all if you have this dimension right here and that is the dimension that we worked from on the female side because that would be the widest part or where the pin registered inside 126 diameter pin against the angle where's the math because you're going to measure across the outsides of the pins what do you use this is really easy you know that this is the radius of the triangle right there the radius of the pin and just like the construction from before right angle right angle bisector there's your triangle 30 60 90. 126 diameter 0.0 [Music] you know that just had it when the marker makes a mistake like that 63 is the radius right the vertical is always half the hypotenuse so this is 126 as well and the base right there calculator around here somewhere base times 86603 gives us 109 on the bottom 109 from here to here radius from here to here there is the double dimension add them up two times whatever the stack is plus the required dimension measurement over the pins height doesn't matter if you're working from the inside corner it doesn't get much easier than that radius gives you the triangle the triangle gives you the base leg base leg plus the radius times two added to the dimension you're shooting for measurement over the pins there you go i will apply that to the cross slide and the carriage components in the next video but i figured it would be a good way to just introduce it to all the triangles and math involved try it with a couple different size pins just work it out you know the 30 60 90 triangles this is not going to work for different angles things are going to change up a little bit these two numbers will not be applicable and remember if you're doing the math and the base leg comes out bigger than the top leg well you use the wrong number use the other number the hypotenuse is always the longest leg in the triangle that's all i got thank you very much for watching thank you very much for the support getting a lot of good messages offline i very much appreciate that if i don't respond to all the comments the volume is a little overwhelming so i guess that's a good thing as much as it is a bad thing because i do appreciate all the remarks shirts are still available on the website check them out and once again we're doing good stay well joe pi advanced innovations in austin texas i'm out you

Channel: Joe Pie

Views: 40,560

Keywords: Joe Pie, JoePieczynski, Advanced Innovations, advanced innovations llc, how to, machine shop, shop tricks, shop hacks, shop techniques, shop tutorials, Pm Research, EL1, mini engine lathe, scale models

Id: Wc0m4BiDXGE

Length: 35min 31sec (2131 seconds)

Published: Mon Mar 08 2021