Author Topic: "Toolpost" drill for Myford  (Read 5253 times)

Offline Allen Smithee

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"Toolpost" drill for Myford
« on: February 19, 2016, 11:11:47 AM »
[started in Rod's handwheel thread but moved here because it was rude to continue there]

To recap - I saw Rod's simple "toolpost" drill (mounted on a milling slide rather than the toolpost, but can't think of another name for it) and thought it looked not only very useful, but also very simple to make. And that started this line of thought:


My usual problem with something like this is simply that I start with a concept for something that will do things I want to do, but within minutes this expands into all the possible things it COULD do (most of which I will never actually need), resulting in a set of requirements that define a design of a hundred times the complexity and/or precision which is such a challenge to make that I never actually do it!

So I've set myself some boundaries. First on the operational requirement:

1. I want to do be able to drill off-axis holes in the lathe, using my currently unfinished GHT headstock indexing/dividing attachment (so that needs to be finished as well).

2. The holes will all be axial (parallel to the spindle axis) so that the unit [held in a milling slide] can be mounted directly on the myford cross-slide "boring table" (not on the compound or the toolpost). The milling slide I'll be using will be this one:



3. Whilst drilling radial holes (90 deg to the spindle axis) might be useful I won't make specific provision for it. I already have some capability in that area because I can mount the mill/drill head from my Unimat 3 dorectly on the myford's cross slide, and anything that needs more than that can be done in my Seig X2p using my rotary table or my VDH (when I finish it - can you see a pattern emerging here?).

4. I want to be able to use drills and possibly reamers from "small" up to about 6mm/1/4" because I don't think the setup would be stiff enough to go much bigger, and this bounds the chuck size. This means I'm looking at spindle speeds in the range 200-6,000rpm, which means it needs ball-races rather than plain bearings. I'm assuming angular contact bearings to minimise the risk of chatter. The only milling capability I want to treat as a primary requirement is the use of slot drills to spot-face and/or counterbore to get flat seats for screws and nuts. This means that I'm probably going to get what I want from a drill chuck rather than needing collets.

5. Whilst being aware that at these speeds I could have some "toolpost grinding" capability it's not something I want to make particular provision for because I don't like grinding in my lathe (the shear amount of work involved in covering and protecting everything and then cleaning down afterwards).

6. Sewing machine motors are OK, but they are expensive and bulky for what they are, so I'm going to try using a cheap brushless motor operating from a 12-18v DC power supply at around 200watts. I've mentioned this before and have a bunch of suitable candidates in my spares boxes, so this is the opportunity to find out if it really does work. If it does this would make for a much simpler/cheaper solution to powering things like the UPTs

7. I happen to have a mild steel block which is 82mmx46mmx46mm that is almost exactly the same width as the milling slide. I think the 82mm dimension would be long enough to give decent support to the spindle, so this looks like the candidate chunk of metal to make it from!

AS
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Offline Stuart

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Re: "Toolpost" drill for Myford
« Reply #1 on: February 19, 2016, 11:24:18 AM »
Allen

Can I chuck my two pence worth in

200w will be more than adducate

Can these motors be speed controlled ?

The two points that are of concern is cooling and the off load speed


It looks to have a lot of potential ( pun intended )

I go for a ARC spindle with suitable collet system you won't need many because you will wish you had


Bearings do they do magneto bearings in the size you need they are cheap and rated to 30 k on oil , used some in my quorn

Just some rambling thought for you to chuck out

Stuart
My aim is for a accurate part with a good finish

Offline Allen Smithee

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Re: "Toolpost" drill for Myford
« Reply #2 on: February 19, 2016, 11:28:15 AM »
I started drawing it up in Solidworks last night, and made some further decisions. Firstly I'm not going to constrain myself to the 12mm shaft to suit the Arc bearings, because I found a supplier with a much wider range at similar prices. So I've decided [for now] that the spindle will be 15mm, currently dithering between mild and silver steel (any thoughts?).

The reason for the 15mm shaft is another decision - I'm going to have a unimat-format M14x1 spindle nose and register. This means I can use the tailstock chuck from my Unimat 3 for simple drilling, and if I need to do more complicated stuff (which I can't think of right now) I can always fit a unimat chuck.

At the moment I'm thinking that the whole unit will simply clam on the jaws of the milling slide's integral vice. I need to check that the jaws of this vice are sufficiently parallel to the lathe's spindle axis, but I don't want to have to dismantle the slide to swap between vice and drill unit. I will make provision (ie drill the holes) for a four-bolt mounting into the slide's T-slots, but I'm hoping I won't need to use them.

I'm also still having one long last think about whether it would be better to actually design it for toolpost mounting rather than milling slide mounting. The milling slide mount will be much stiffer, but popping it into the QCTP would be much quicker and more convenient. It would also add the capability of drilling non-axial holes and milling at funny angles using the compound slide, which the milling slide mounting won't do. The real question is would I really ever need to do this...

Any thoughts on whether I really need the extra stiffness of the milling slide mount?

AS
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Offline Allen Smithee

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Re: "Toolpost" drill for Myford
« Reply #3 on: February 19, 2016, 11:51:54 AM »
Can I chuck my two pence worth in

Absolutely. The point of me writing these brain-dumps is that I'm a clueless newbe at most of this stuff, and I'm hoping the experienced chaps and chapesses will be chucking in their tuppances whenever I suggest something stupid (ie at least 10 times a minute).

Quote
200w will be more than adducate

Can these motors be speed controlled ?

Yes, but it's a qualified yes. The brushless DC motors used in (fregsample) the better variants of the Seig lathes and mills are actually run as synchronous motors - the controller varies the switching frequency (field rotation rate) to control the speed, so they run will maximum torque regardless of speed. The torque on my Seig X2p at 150rpm is awesome, and no need to change belts on pulleys or gears on shafts, ever.

The sort of motor I'm looking at has a speed-controller, but it operates using pulse-width modulation, which is a fancy way of saying it controls the speed by dropping the power (not strictly true, but a reasonable approximation). So at low speeds the maximum torque is less. They compensate for this by having what you might think of as "cruise control throttle maps" built into the controller, and one of the things I'm keep to find out when I do this is just how effectively they can really work at low speeds. To partially compensate for this I'm looking to use a motor with plenty of headroom - something in the 200-300W range rather than the 90-100W sewing machine motors which are usually used for this sort of thing.

If it does what I hope it will do then these will be idea motors for "masthead mounting" on things like UPTs - these motors are very small (35mm dia by 45 long for one of the bugger ones), but it may not work! As a fallback option I can fit sets of coned-pulleys, and if that doesn't work I can go down the sewing machine motor route.
 
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The two points that are of concern is cooling and the off load speed

I'm intending to mount the motor inside a but of plastic tube to keep the swarf away, and I'm thinking of putting a cooling fan on its shaft to draw air through the tube when it's running, so I'll have to see how well that works. The "throttle map" thingies I mentioned above should mean that the difference between off-load and full-load RPM is no more than 20% (typically 10%), but that's when turning a propeller. Whether this holds true inthis application is something I'm looking to find out!

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It looks to have a lot of potential ( pun intended )

That's my current thought as well... ;D

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I go for a ARC spindle with suitable collet system you won't need many because you will wish you had

The reason I'm shying away from the collet option is that the main use I wasn is drilling, and using ER collets to hold drills is frankly a pain in the butt because you have to change so much to move between drill sizes. I'm looking to use a keyed (rather than keyless) drill chuck for similar reasons - it would actually be more convenient when you look at how the thing is mounted and where you're putting your hands.

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Bearings do they do magneto bearings in the size you need they are cheap and rated to 30 k on oil , used some in my quorn

That site I linked to above seems to have a range of both angular contact and magneto bearings - in these sizes the prices are similar.

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Just some rambling thought for you to chuck out

Please keep rambling - it's all useful info!

PDR
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Offline tangler

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Re: "Toolpost" drill for Myford
« Reply #4 on: February 19, 2016, 01:33:57 PM »

The reason I'm shying away from the collet option is that the main use I wasn is drilling, and using ER collets to hold drills is frankly a pain in the butt because you have to change so much to move between drill sizes. I'm looking to use a keyed (rather than keyless) drill chuck for similar reasons - it would actually be more convenient when you look at how the thing is mounted and where you're putting your hands.


I've actually gone the other way on both my mill and the milling spindle.  To me, it's more of a pain to change the chuck rather than the collet so now I do all my drilling using either the ER25 or ER11 collet.  The reason I bought the straight shank ER11 spindle was to fit into a 12mm collet in the ER25 to get into those intimate little places where the ER25 collet nut can't go.

Decision, decisions  :-\

Rod

Offline Stuart

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Re: "Toolpost" drill for Myford
« Reply #5 on: February 19, 2016, 01:52:59 PM »
Allen

Yes I am aware of the types of brushless DC motors I have two in the WS one on a SX3 and the other on a KX1 the former causes a lot of consternation in that the spec it as 3phase DC . They both work with Hall effect sensors feeding back the position of the rotor and the electronics switching the stator coils as and when .

The other type you mention do not use feed back and rely as you say on PWM for control gues they are from RC planes or WHY

Good luck with the project I will be watching but please reconsider the use of a collet system

If you go with AC bearings I would make the spindle like a quorn with the pre load applied wit six light springs 15 pound total will be more that enough

Stuart
My aim is for a accurate part with a good finish

Offline Jasonb

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Re: "Toolpost" drill for Myford
« Reply #6 on: February 19, 2016, 03:25:40 PM »
You could machine the spindle bore to suit ER11 collets which use M14 closing nuts but would have to make the nut as they are 0.75mm pitch rather then the Emco 1.0mm, you would get the best of both words and very little overhang when using collets

Offline Allen Smithee

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Re: "Toolpost" drill for Myford
« Reply #7 on: February 19, 2016, 03:42:48 PM »
The other type you mention do not use feed back and rely as you say on PWM for control guess they are from RC planes or WHY

[mode = control engineering pedant]
Strictly speaking they do have feedback - they use the back-EMF pulse from the magnets passing the stator to time the next phase-switch; it's a different mechanism to achieve a similar result, but it means that although the timing has feedback the speed control law is open-loop.
[/mode]

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Good luck with the project I will be watching but please reconsider the use of a collet system

I'm still looking at the M14+chuck, sorry! For the accuracy I need the extra faffing in swapping drill sizes with collets is just too much of a downside, never mind the 80+ for the chuck, spanner and collets.

If I need more precision later I can always make another spindle!

I'm actually coming more and more to think that mounting it in the QCTP might be a better idea. Maybe I'mm make provision for both options.

AS
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Offline tangler

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Re: "Toolpost" drill for Myford
« Reply #8 on: February 19, 2016, 04:50:23 PM »
My milling spindle arrangements have evolved somewhat over time.

This mounting block uses a locating wedge cone similar to the topslide.  It is sized to mount the spindle exactly on centre height





But there isn't enough movement of the cross slide to get the spindle to the lathe centre so I added this extension.







That worked fine and it should be possible to permanently mount a motor to have a quickly mountable solution - almost as quick as changing a tool holder but probably more rigid.

I had bought the original milling spindle from Arrand many years ago.  When I saw the Myford fixed vertical slide and "home made" milling spindle advertised on ebay by Myford (the new people don't seem to know much about the model engineering world) I snapped the 2 up for 80 - I recognised the spindle as an Arrand.  The original spindle is still used for odd things like gear cutting, where I have to use a countershaft to bring the speed down in order not to destroy the cutters.



Some ideas for the mix.

Rod




Offline Stuart

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Re: "Toolpost" drill for Myford
« Reply #9 on: February 19, 2016, 05:01:23 PM »
Allen

Stupid me forgot my first principles it's been a long time since I used them

I finished my working life as a controls eng but in HVAC I used to design local control units for AC or WHY and write the BAS software to run them

Different to what I first studied


As you said you threw it out to the great unwashed for their cogitation but correctly it's your job , your money and your choice

Have fun I look forwards to see what you do in the end


For doing the same job in the Myford I chickened out and made a mount for my fordam high speed flex drive for the tool post hang it up stomp on the pedal and away I go

Stuart
My aim is for a accurate part with a good finish

Offline Allen Smithee

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Re: "Toolpost" drill for Myford
« Reply #10 on: February 19, 2016, 06:10:22 PM »
More food for thought, chaps - much appreciated!

So if I want it mounted on my QCTP I could actually make it "multi-mountable" by having a piece of 1/2" square steel bar bolted to the side of the main block, probably in a small rebate to assure alignment, as well as having those main mounting holes to engage with the T-slots in the milling slide in addition to the ability to simply clamp it in the slide's vice. At least I think I can - I need to sketch it out and see if I can have all three options without having to move the motor/countershaft assembly. Ideally I want it to be a completely self-contained unit that I can just pick up and bung on almost as easily as swapping turning tools, but I'll have to see what's geometrically possible!

I'm looking to have a countershaft so that the final drive can be belt drive, but the motor bearings have minimal side-load. The motor would drive the countershaft via gears - I have a box of nice chunky strong plastic ones that would probably do the job as well as giving me the option of having change-gears for two or three different speed ranges should I find that these motors have asthmatic low-speed torque. The motor I have in mind, if driven from a 12v supply, would need something like a 2:1 final drive ratio for the highest (6,000rpm speed), so if I want it to also do 200rpm I suspect I'll need those changeable gears.

I'll try and draw this up in solidworks over the next few days and post some pictures here for a design review(!)

AS
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Offline Bertie_Bassett

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Re: "Toolpost" drill for Myford
« Reply #11 on: February 19, 2016, 06:55:18 PM »
just for another take on things

I designed a small milling spindle for my lathe a year  or so ago, based on a brushless outrunner motor and a cheap ER20 collet chuck running in 2 double row AC bearings. I only got as far as test running things, and have yet to actually finish it. but it looked promising

I designed it so that it replaced the tool post on my lathe and had its own vertical slide of sorts for height adjustment.

I was planning on using it for light milling aswell as drilling  hence the use of collets.

heres a couple if pics if its of any interest










one day ill finish a project before starting another!
suffolk - uk

Offline Allen Smithee

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Re: "Toolpost" drill for Myford
« Reply #12 on: February 20, 2016, 02:52:21 PM »
Before I commit to a decision...

According to various data sources on the web, A JT1 taper angle is between 2.1953 and 2.2074 degrees (per side). Can anyone advise how close this has to be for the taper to grip properly? Is it +/- 0.1deg, +/-0.01deg or what?

AS
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