Power Drawbar and Tool Offsets (DIY CNC Mill Upgrades 2)

it's almost gentle on the way it releases the slug out of the collet that's awesome dr d flow hey what's up guys it's dr d flo and i'm back with another upgrade to my cnc mill that i think you're going to enjoy but first we need to talk about how i change out tools between operations when i first got the mill i received a set of r8 collets for this type of tool holding there has to be an exact match between the collet diameter and the tool shank diameter tools could be as small as 1 8 of an inch and as large as three quarters of an inch as a tool change example we will use this quarter inch mill drill and quarter inch collet this is the draw bar it threads in to the bottom of the collet it up into the spindle now the taper on the collet will cause it to close down on the end mill i start off by getting everything finger tight so that the tool doesn't fall and hit the table now this precision matthews 833 tv mill has a major design flaw there's no spindle break or flat on the spindle nose that i can grab onto to stop it from spinning when i'm tightening the drawbar precision matthews has been relatively quiet on this issue and i think they suggested using a rubber wrench to stop the spindle from spinning now this rubber wrench is too big because i don't actually use this method but i guess it would work albeit it would be a hassle i've opted for the more dangerous approach to tightening the power drawbar which is turning the motor on a low rpm to oppose the tightening of the drawbar here we have it at just 50 rpms however if i accidentally turned off the motor while it was still set to a high rpm that would be an incredibly dangerous situation right the wrench could fly off the power draw bar or i could get sucked into the mill neither which are good so besides this motor method being dangerous it's also not very repeatable when it comes to the holding force of the tool i've actually had a couple end mills get pulled out of the collet because the cutting forces were too high people have semi-automated the tightening and loosening of the drawbar with an electric or air powered ratchet this method would result in a more repeatable holding torque but it wouldn't work for my mill because i still don't have a way to prevent the spindle from rotating when tightening down the drawbar and i'm not using a rubber wrench a pneumatic or powered drawbar is a much better solution for my setup if you're not familiar with the power drawbar it'll make more sense when you see it in action but briefly here's how it works an air cylinder presses down on the drawbar to unseat the collet when you go to change out tools and when you're ready to cut springs pull the drawbar up at a constant force bringing the collet into the spindle securing the tool i initially had plans to put together my own power drawbar but the build requires a longer drawbar than i already have i don't have a lathe to turn down just apart and it was actually more economical to purchase a kit from priest tools than to have the local machine shop make me a drawbar also greg from priest tools has already worked out all the physics so we should have the perfect amount of holding torque for this mill let's meet over at the bench to talk about all the components that make up a power drawbar so here's everything that comes with the kit we've got bolts and spacers mounting plates a switch for turning on the drawbar which is connected to a limit switch more on this later and also an electric solenoid we have some tubing we have the air cylinder we have belleville washers a collar a new drawbar and some anti-seize lubricant the air cylinder might be the most important part this is a two stage air cylinder with a hundred millimeter bore with a two stage air cylinder you get much higher forces and a more compact design if you've seen other videos of people installing power drawbars they often have to include a lever arm to amplify the force of their cylinder we don't have to do that for this cylinder which simplifies the design i'm actually going to hook this air cylinder up really quickly just to show you how it works so both of these tubes connect back to the solenoid and this clear tube will connect to my compressor here's the hose for my compressor the air is at 120 psi now this cylinder can will work at 90 psi it'll be able to apply less force when i flip this switch to the on position it lights up but nothing happens that's because the limit switch also needs to be pressed this is a safety feature and i'm going to talk about where it goes in the assembly later on i'm going to go ahead and click this with my finger and as you can see air is supplied to the cylinder and it rises up out of the housing when i release the limit switch the solenoid cuts out releasing air out of the cylinder now this is a single acting air cylinder so it needs to use gravity or a spring to bring it back down to the start of the stroke that leads us to our next component the bellville washer believe it or not these conical shaped washers are very powerful springs they are more useful when stacked with other bellevue washers you can stack them in parallel where they are all facing the same direction or in series where they alternate directions in a parallel configuration you can get a stiffer joint but maximum deflection of the entire stack equals that of a single belleville washer in a series configuration the amount of deflection will scale with the number of washers the series configuration is particularly useful when you want a lot of travel in your spring joint which we do need i do want to point out that you can get almost an endless number of spring constants and deflection amount by stacking them in combination of both series and parallel greg's already done the math for us and we need eight billville washers stacked in series this will give us enough deflection that the collet will pop out of the spindle and release the tool but it'll be stiff enough for up to 34 foot pounds of holding force we will cap off this stack with a little collar and i will talk about the function this collar plays in a second but let's go ahead and install the new longer draw bar on the mill so we need to remove the face plate and the sheet metal up here that's protecting the belt drive you actually have to lower the quill to get this piece out remove the current drawbar and call it applying the anti-seize is a little bit messy so i'm gonna throw on some gloves start by putting a little bead the lubricant on the head the drawbar with these belleville washers it's kind of hard to see their concavity until you start stacking them in this series configuration where there's a little bit of space in between each unit the space will be taken up when the stack is compressed the last component that needs some anti-seize is the collar we'll flip the whole assembly upside down all right so i went ahead and switched gloves we need to rub a little bit of anti-seize on the outside taper of our collet we want to be really careful not to get the anti-seize on the inside of the collet because then her tool will slip you want this collet to be able to pop right out when the air cylinder presses on the draw bar nice light coating on go there and switch gloves one more time now this next step we're going to pull the collet fully up into the spindle and we're going to actually set the holding force so we need to insert this slug because you don't want to compress the collet without a slug in it because it'll stick okay that's finger tight these are the instructions that came with the power drawbar kit we got the drawbar hand tight but now it's time to tighten it down further and compress those belleville washers to get significant holding torque this table right here tells us how much holding torque we get for each 1 6 of a turn of the draw bar i'm going to shoot for two full turns to get 32 foot-pounds of torque because i do have 120 psi compressed air so once i took off the cover i noticed that the pulley has some indents for a spanner wrench so that i can hold on to that i was worried at first i was going to have to use that rubber wrench to set the holding torque but fortunately i don't have to do that keep an eye on this spacing you should see it compress yeah that's that's one term that's two you can definitely see that that space got much smaller those washers are being compressed and in turn we're gonna have a lot of force keeping that collet and that tool where it's supposed to be next we need to install the base plate the other components will attach to this another awesome feature about this kit is that it uses the existing mounting points so you don't have to drill any new holes in the casting of the mill next we need to do the cylinder assembly we're going to head back over to my bench to put that together so cylinder attaches to this plate through these big bolts and spacers i think these other holes are for if you opt for the smaller cylinder i thought it was symmetric there for a second this edge is actually slightly longer and it should be next to the air inlets are you kidding me my 3 8 allen key is not big enough that's probably a half inch i don't keep that on hand i'm gonna have to purchase a half inch for later so hopefully finger tight will do for now so now we need to attach this assembly with these bolts and these two black spacers to the base plate this is going to look a little bit funny with only one side having spacers but it'll all make sense in a second so here's the weird part this whole assembly is floating and trust me that's by design you don't want the force of the cylinder translating to the bearings that are within the spindle they're not meant to withstand that kind of axial load so here's the trick this plate slides into these dovetail grooves and goes around the collar when the air cylinder presses down with its force this is going to pop up but it can only go up so high because this piece is trapping it so effectively you're just pinching this area the force is restricted right here and the spindle bearings aren't going to feel any of it it's it's ingenious it's really awesome that you can take a mill without a power drawbar and retrofit one with a relatively simple assembly um and you can reap those benefits it's really cool i hope you can now understand why this plate which is known as the actuator plate is so important if it's not present if it's not engaged underneath the collar when you turn on the power drawbar that force we translate to the bearings now to prevent that from ever happening this kit has a trick up its sleeve remember that limit switch from earlier and how i said it was a safety mechanism well the electronics are set up in such a way that the power drawbar won't actuate unless the limit switch is triggered and the limit switch can only be triggered when the plate is fully engaged i'm going to go ahead and install that now i love it it's idiot proof when you're working on a part that requires like 20 different tool changes your mind is going to be preoccupied and it's nice that you know if you forget to engage this the power drawbar is not going to turn on we can go ahead and attach the rest of the electronics so they can stop dangling the nice part about this manifold that i set up in the last video is that these two outlets are unregulated so they're going to be at 120 psi [Applause] so we can adjust this bolt that's screwed into the shaft we want to be just above the draw bar so it's not rubbing when it's spinning all right it's time to flip the switch and hopefully that aluminum slug will drop out of the collet here we go yes that's awesome will it grab it yup no problem let's do it again it's almost gentle on the way it releases the slug out of the collet that's awesome man this is obviously way safer than the motor method it's way quicker it's awesome i don't know why it took me almost a year to do this upgrade sweet i just need to still tidy up all of these tubes and the power cord for the drawbar i'm going to save that for a later date because i just want to keep rolling with this project in this video the one downside of the power drawbar is that it's much more difficult to switch between r8 collets you would have to reset the compression on the belleville washers every time you want to switch to a tool with a different shank diameter but there's a solution enter the tormach tool system or tts for short perhaps you thought you'd be able to avoid paying the tormach tax if you want the diy route unfortunately these tool holders are just too good to pass up their operating principle is simple one end is a 3 4 inch shank and the other end is a tool holder you have a couple different options for holding the tool from an er collet to a set screw holder and even a jacob's drill chuck to be clear i'm in no way sponsored by tormach i'm just highlighting an invention that made cnc milling with an r8 spindle way more convenient because you can rapidly switch between tools without having to switch out the collet because all tts holders fit into a 3 4 inch collet which is the size that is currently installed for my power draw bar setup check out how quickly i can switch from a roughing end mill 2a finishing in mill to a drill it's a little tight the tts holders are a natural pairing with the power drawbar if you've seen some of my past videos then you will know that i have been using the tts holders for quite a few projects even without the power drawbar because these holders allow for repeatable tool offsets when you're swapping tools in and out of the spindle for the second part of this video i wanted to give an intro to setting tool offsets just fyi this section is aimed at the beginner and will not cover the extra precautions needed for high precision work when you first start running your cnc mill or even cnc router you usually set your zero which is typically when the end of the tool is touching the top of the stock material by placing a sheet of paper or feeler gauge on top of the material and lowering the z-axis until you feel resistance when you tug on the paper you can account for the thickness of your feeler gauge or paper defined z0 there are two problems with this approach the first is that it is subjective because your definition of resistance may change from tool to tool and stock material to stock material which affects accuracy the second problem is that this method is slow the quickest and most accurate way to find zero is to touch off the top of the stock material with a digital or analog probe and then compare the length of the probe to the length of the next tool and add or subtract distance accordingly now what is length referring to we need a reference point to measure our tools from the most logical point to measure length from is the bottom of the spindle nose because this point is accessible and its position is always known after a homing cycle so the length of the tool will actually include part of the tts holder or the body of the probe our first objective is to find the length of the probe this can be a little tricky because we don't need to know the static length we need to know the length of the probe when it detects an object in the z plane which means the probe length will be slightly shorter than it is now there are a couple different ways to find the probe length some of which don't require any fancy tools the only wrong way to set the length will be to touch off the probe tip on the touch plate this would result in an erroneous probe height because both the touch plate and probe move and it would be impossible to know how much movement was a result of the plate versus the probe i personally use this analog touch plate to find the probe length the following process first i use a gauge block to bridge the post on either side of the touch plate depressing it in the process i set the indicator to read zero at this point and then remove the gauge block next i bring the spindle nose down until the indicator reads zero again the spindle nose is now at the height of the post i will set this as my reference point and record the absolute machine coordinates i will then load my digital probe into the spindle and have it find the z height of one of the posts this will change the offsets in my g54 coordinate system but i can recheck the machine coordinates for the new z value which can be compared to the z value from when i touched off the spindle nose to find the length of my probe this method there's only one moving part now because you have to own a manual tool setter for this method you could also use this instrument to find the offsets for your tools and it really doesn't take that long this is the reason i say the digital touch probe is not mission critical however i do find the digital touch plate to be convenient so let's go over that process quickly similar to the analog touch plate we bring the spindle nose down until the touch plate alarms this is the reference position and from there we can touch off tools one at a time for each tool the software compares the z position of the tip of the tool to the spindle nose to find the tool length each tool length is stored automatically in a digital table which prevents any transcription errors that can occur when you have to manually enter tool lengths in a table i leave a little note next to each tool so i don't confuse them the digital touch plate is always sitting on the table even during cutting operations and chips will stick to the top of it if the chips are not cleared off the next time a tool is touched off the wrong length will be calculated because what was measured was the length of the tool plus the thickness of the chips underneath it to automate the cleaning of the touch plate i installed some pneumatic tubing that will supply a blast of air prior to touching off the tool the air is controlled by an electric solenoid that i have mounted in the back i will upload the macro file and wiring diagram to my website if you want to try out this upgrade for yourself if you're thinking about purchasing building or converting a mill then i strongly suggest checking out my cnc mill web page i've spent a lot of time writing down everything i've learned from my conversion to share with you and with that i'm going to catch you guys in the next video which may or may not be my next planned cnc mill upgrade you're going to have to subscribe to find out have a good one

Channel: Dr. D-Flo

Views: 45,334

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Id: 6KaNF0IshBI

Length: 24min 1sec (1441 seconds)

Published: Fri Jan 29 2021