First off - sorry if this is in the wrong forum! I don't post very often.
To business: Just as a hobby endeavour, I'm going to design a medium size spindle for an imagined (later to be designed) 5 axis gantry-type machine. I have a few goals: design a spindle which is as mechanically sound as possible (so that, if one were to build it, it would work) and a spindle that I actually like. There are a couple of things I'm aiming to do, right off the bat: first, I want to use a frameless BLDC motor mounted on the spindle as the drive. Something like Parker's SKW073_XXXLAM (pdf link) motors - these are relatively high-power but small (the smallest motor produces 3.1 kW of output power in a package 80mm in diameter and 114mm long!). I like the concept of the spindle being an all-in-one unit, with only one moving part: the spindle itself.
I'm aiming for a BT30/ISO30 taper. I'd also like to do a power drawbar so that the spindle is ATC-ready. I've read other people having trouble with power drawbars pushing the toolholder offcenter due to the balls in the gripper not properly centering, to avoid this I'm thinking a floating gripper is the best bet - where the gripper is secured to the drawbar by something like this, so it can pivot. My starting question is: does anyone know where I can find the specification for the BT30 taper? As a follow-on, is there a certain kind/shape of pullstud I should design the gripper for?
This design is currently only a sketch on engineering paper, but I'd like to go all the way through CAD drawings as an exercise, and actually do the calculations on estimated cutting forces and deflections. If somebody can tell me where to find the taper specification, I can start drawing something for real. As a side note - is a labyrinth seal the only good way to keep chips/coolant/etc out of the lower bearings?
Ideally this is a solid design that I can sit on until I have the financial resources to actually build one, so I'm aiming for the best spindle I can design.
Hey Jacob,
Yeah I figured. I work with similar equipment, so I wasn't anticipating a low-cost spindle. Like I said, this is 99% just a design project. I want to design the best midsize/small spindle around. I'll work on building it when that becomes possible.
Thanks,
Sam
I am currently in the machining stage of just the same thing.
I have designed a BT30 ATC spindle I have currently made the shaft, gripper, draw bar and internal tube with taper for the gripper ball bearings and spring washers and just have the housing left to make.
The design is pretty good in my opinion and I think there is a lot to be learnt from that thread. Helped me a lot in my design and mine it is very similar. Big thanks to H.O by the way as he may not realise how much help it was to me.
As for taper dimensions, type in BT30 taper dimensions into Google and select images and you will find them quicker. taper is 7/24 if I remember correctly but don't quote me on it.
As for the pull stud, I when with a 45degree pull stud and dimensions can be found the same way.
The shaft will need to be made from a steel that can be hardened off course or go the route I did and use 4140 pre hard. It is around 28-32 HRC
It saves the worry off distortion beyond what is left for grinding, although if your experienced in heat treating im sure this isn't a issue but I am not.
Another thing I will add is to look at the cost off bearings as you may be surprised at the cost off them, depending what speed you want the thing to run off course is a big factor.
Also at high speeds you will need to think about balancing the spindle too.
I have also come across posts where the gripper is pulling the tool off centre, although I don't see how if there is enough upwards force pulling the holder into the taper. But im sure they are not lying!
Hope this helps a little, just some off the things I learnt along the way.
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Spindle Design Project
