Two sorts of spindle feedback.
I am amazed that it is so long since I updated this thread, and equally amazed how little progress the actual machine has made in the last year.
This is partly because I spent a lot of time sailing (crossed the Pacific) and partly because I have been working on the software side of things.
So, an update. I have one axis working. But to get the other axes working with the drivers I have I need to update their firmware, and there is no Linux tool for that, so I am writing one.
I will post about that, with pictures and possibly video later.
The subject of this message is spindle feedback. It is handy for closed loop spindle-speed control (though I don't think spindle speeds have to be _that_ accurate). It is imperative for rigid tapping and gear hobbing though.
The Harrison Mill is a "Universal" mill, with a horizontal spindle and a vertical adapter. The mills came with two options of motor-to-gearbox pulleys and two vertical adapter ratios. With both fast ratios you have 100 to 2500 rpm. Guess which ratios I have? I have 47 rpm in the lowest gear, and 1000rpm in the highest. The VFD lets me boost that a bit.
In the long term I hope to make a pair of the high-speed vertical gears. You simply swap a 51:51 set for a 36:66 set inside the head rotate housing. However, that means that the spindle feedback needs to be in the head.
I decided to use some Allegro ATS667 devices running off the gears in the head:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/50sU9lCdX6QIFUW_s5hL5tMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-JCUbsnHBHEk/UBXHQ-X6MGI/AAAAAAAABWo/losy8vN60Ak/s144/IMG_0432.jpg" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/CNCUnsorted?authuser=0&feat=embedwebsite">CNC-unsorted</a></td></tr></table>
These are (as far as I can tell) unique sensors that contain a magnet and a Hall device, and can detect anything magnetic with logic output.
[url=http://www.allegromicro.com/Products/Magnetic-Speed-Sensor-ICs/Transmission-Sensor-ICs/ATS667.aspx]Allegro MicroSystems - ATS667LSG: True Zero-Speed, High Accuracy Gear Tooth Sensor IC[/url]
I bought some from eBay as I could not find a UK stockist. Then I mounted them in a bracket on the head cover:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/wE4cF0uBYu-pY5vFeuI00tMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-fdL-UsqLqFA/UBmgXnit-hI/AAAAAAAABYU/y9YCcurePp4/s144/IMG_0436.jpg" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/CNCUnsorted?authuser=0&feat=embedwebsite">CNC-unsorted</a></td></tr></table>
The one at the bottom is for the index, it picks up off of a screw I put in a handy tapped hole on the spindle.
Because the sensors are running in oil, I needed an oiltight connector. Lemo connectors are lovely things, and vacuum-tight, so I used one of them.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/xLQQyKpGjW-i3pr9W9F89NMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-J_CgVepAcnU/UBmgbu1V1NI/AAAAAAAABYE/5o5yZ9Na_bE/s144/IMG_0437.jpg" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/CNCUnsorted?authuser=0&feat=embedwebsite">CNC-unsorted</a></td></tr></table>
Hang the expense!
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/zH4KytVy-QaXID3OzoUXeNMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-68Sw0HcB0U4/UBmgfe0Tr9I/AAAAAAAABYM/E9hoIL2LpqY/s144/IMG_0438.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/CNCUnsorted?authuser=0&feat=embedwebsite">CNC-unsorted</a></td></tr></table>
It works very nicely, and I have spindle speed feedback and an interlock which prevents the pneumatic drawbar activating when the spindle is spinning.
Squeezing in a bigger screw
I have always been rather conscious that the 12mm Y-axis screw and standard-clearance ballnut probably wasn't really ideal, but I din't think I could fit anything more in. Then I found that GTEN list an RSH nut that is only 1" diameter in the 16mm ballscrew size. The existing RSW 1205 nut is 25.5 diameter, so I could have a bigger screw and a fractionally smaller nut. I also found that the factory were able to supply it special-order as a preloaded variant. £100 for the ball and the screw, but I decided to go for it.
When it arrived it looked a lot beefier than the 12mm, a serious improvement:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/XLMGb2yLNvqkK70U11MJ7dMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-YQzCXuoJkRY/UqEMpWhLWuI/AAAAAAAACyw/MBEtnYPk49s/s144/IMG_0779.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
However, when I unwrapped it, there was a nasty surprise.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/TToLLpPtd1N2Gx-mynggUtMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-qr4iwgbhueU/UqEMqMSXSAI/AAAAAAAACy4/kfjheJqE_q0/s144/IMG_0785.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
The new nut has an external ball transfer tube not shown on the drawing in the GTEN catalogue! This seems like something of an oversight to me.
The nut and screw sat in their box all summer while I tried to decide what to do. Eventually I got the CAD out and started to play, and I worked out that I could _just_ squeeze it in. The tube meant that it couldn't screw into the housing and lock with a nut like the RSW nut did, it would have to be a split housing with clearance for the transfer tube.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/ku1VIKupjIF3SwbYoYN909MTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh4.googleusercontent.com/-udwfLklZBv0/UqEMnThRkaI/AAAAAAAACyg/M8YYWQjBvEo/s144/IMG_0774.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
One advantage of this is that I do at least know the orientation of the nut in the housing. The Harrison has an oil nipple for the leadscrew (with a complicated drilling to get the oil to the bore where the nut is attached). The transfer tube isn't oil-tight, so works nicely to get oil into the nut. That is what the secondary little hole is for.
This is it all bolted up around the nut:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/IW-gjgoxv4E2IOZdrj4hkNMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-bjBDZE3Nto4/UqEMrvkXN7I/AAAAAAAACzI/nE_s2Z5B5Nk/s144/IMG_0791.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
You might be wondering what the taper on the end of the screw is for. There is a bit of a problem with assembly:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/ezpd2gtGljk1WyDEkfw9idMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh4.googleusercontent.com/-HCJ34YyVteA/UqEMsogsRwI/AAAAAAAACzQ/HMW2ekXY9WY/s144/IMG_0795.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
The original leadscrew simply went in from the front. Not an option when you want to put the nut and the screw in as an assembly (trying to assemble the nut onto the screw inside the knee of the machine seems not so much to be tempting fate, as poking fate with a stick and calling it rude names). So I borrowed a brilliant idea from Wohlhaupter. (I did the same with the 12mm screw). I machined a taper on the end of the screw (Ballscrews are really fairly easy to machine with CBN at 120m/min. It's moderately spectacular too.) There is a matching taper in the socket, and the socket has a M10 x 1.5 thread in it.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/qzxm1XbHqIUZS5GCtz1CCdMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-woUy-AI-Aq4/UqEMogqn3uI/AAAAAAAACyo/vUBgpkidrXE/s144/IMG_0775.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
The screw has an M8 x 1.25 thread in the end, and I made a special 2-thread socket screw. The screw goes in the end of the ballscrew, the socket is screwed on until snug, then the special differential screw is backed out using an allen key up the end of the shaft.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/Gu1YtXinbAdzUHSIB5aBAdMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh4.googleusercontent.com/-m7movSmjI0A/UqEMuG7OkfI/AAAAAAAACzg/FW5H15f5hPM/s144/IMG_0799.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
Because the M10 thread is coarser than the M8 thread the effect of this is to pull the two parts very snugly together, as if by using a 0.25mm pitch screw. It also means that I just need to screw the screw back in again to push the taper apart.
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/i0nmI4mYbTEeNgR8m-_f7tMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-7iC_M9tX-hU/UqEMuzU4rBI/AAAAAAAACzo/ZhXbNIce9Ds/s144/IMG_0801.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
On with the swarf-shield:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/5UZI2W8BDMIhhgEybHfF9NMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-XwFUMrSQ7So/UqEMvTq6o6I/AAAAAAAACzw/GjaO48ElTOk/s144/IMG_0805.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
And the servo-mount casting and drive system:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/v07I2fUTNO7sQWMiL99_LtMTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-dCuJ86CNoX4/UqEMxBe7VLI/AAAAAAAACz8/dCi-Ik3vuGw/s144/IMG_0809.jpg" height="108" width="144" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
The handle is just used to move the table by hand for jobs like checking the Gib resistance. It pulls out, and drives the screw by means of a really quick and easy sort of dog-clutch that I found in Machinerys Handbook:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/orn2DIhPXbFz8xbSTZXuf9MTjNZETYmyPJy0liipFm0?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-_AMVzTdwhk4/UqEMwM_17ZI/AAAAAAAACz0/KWx0VR0KoC8/s144/IMG_0807.jpg" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/108164504656404380542/HarrisonMill?authuser=0&feat=embedwebsite">Harrison Mill</a></td></tr></table>
By this time it was getting late, so no test cuts yet. I did find one issue, but a very minor one. The saddle now runs to the limit-switch, because the new screw is 15.08 mm pitch, and I forgot to change the scale setting...
Re: Harrison Universal Miller Conversion
Great project and fantastic work! Would you share details of your steady screw-driven nut assembly? any dimensions for reference? I wonder how you made it so compact. What bearings did u use - a pair of AC bearings? Mated/preloaded in the factory or preload is provided by you by means of some sort of shims? Have you got more photos of your conversion? I bet many wants to see as much as possible:) What size ball screws did u use for XYZ? XY are 12mm dia?? I thought they are way bigger by the photos. And please reveal some details regard that ATC gripper - what steel, how did you machine split grippers, what hardness after tempering, what belleville springs, how many and what pulling force you have? So many questions but you've made SOOO interesting project!
cheers
Bogi
Re: Harrison Universal Miller Conversion
[QUOTE=bogus105;1951772]Would you share details of your steady screw-driven nut assembly? any dimensions for reference? I wonder how you made it so compact. What bearings did u use - a pair of AC bearings?[/QUOTE]
The 3D model of the parts can be found (and downloade din various formats) from [url=http://a360.co/2dJNHJ7]Unsupported Browser ~ A360[/url].
The bearings are double-row angular contacts, but used and preloaded as single-row. (basically with a wasted row) because that was the only way to get a small-enough section bearing. I probably made it a bit too compact, and would have been better letting the ballnut protrude into the space under he table and have a bit more material around the bearings.
[QUOTE]Mated/preloaded in the factory or preload is provided by you by means of some sort of shims?[/QUOTE]The bearings are preloaded by adjusting a threaded collar. There are slots in the inner bearing sleeve and one more slot in the collar to give a vernier-style adjustment. A wire clip fits into one pair of slots to lock it. I didn't bother making 3D models for the threaded collars that clamp the bearing outer-races into the main casting and that clamp and preload the inner races.
[QUOTE] Have you got more photos of your conversion? I bet many wants to see as much as possible:) [/QUOTE] If you click the album link in the small thumbnails above you should get (pretty much) all the photos I took.
[QUOTE]What size ball screws did u use for XYZ? XY are 12mm dia?? I thought they are way bigger by the photos.[/QUOTE]
No, only the Y was ever 12mm, and that was later expanded to 16mm. The X and Z axes both use 25mm ballnuts.
[QUOTE] And please reveal some details regard that ATC gripper - what steel, how did you machine split grippers, what hardness after tempering, what belleville springs, how many and what pulling force you have?[/QUOTE]
The ATC gripper is made from BS1407 tool steel (also known as Silver Steel). The split collet was made by clamping together 4 pieces of square material in a 4-jaw chuck. I then turned a short section and pressed on a collar and centre-drilled the end (actuallly into the 4-way intersection, the collar was needed to stop the lathe centre spreading the bars.) It was then moved further out of the chuck to machine the outside profile. I then cut off the excess and held it in a collet while I machined-off the collar and machined the inner profile. when it was removed from the collet I was left with 4 separate petals.
Re: Harrison Universal Miller Conversion
Thank you Andy for reply. Now i get the concepts behind the driven nut. I came to the same conclusion (4 squate pieces) when thinking about ATC grippers. Did you use Silver Steel for rod and other elements to be hardened? Ball screws are from GTEN (taiwaneese?) or some chineese sort or what?
cheers
Re: Harrison Universal Miller Conversion
I used silver-steel for the round parts of the ATC gripper and the central rod. The outer tube was some thick-wall hydraulic pipe drilled-out and machined on the OD. The end where he gripper lives was hardened silver-steel, screwed in to the tube with (IIRC) a 14.75 x 0.9 mm thread. With a CNC lathe I wasn't limited by standard threads, so chose one that gave me a 1:1:1 split through the threaded region.
I suspect that I made the actual gripper petals out of key-steel, having proved that it could be hardened. Or I might have later-on re-made them with square silver-steel. It's been quite a long time since I did that part.
(Key-steel is .55% carbon, silver steel is 1%.)
GTEN is a Chinese brand of ballscrew. But one with at least a name, and a reasonable reputation.
Re: Harrison Universal Miller Conversion
[QUOTE=andypugh;1952732].... But one with at least a name...[/QUOTE] :D:D
I wonder how did you drill-out so long hydraulic pipe accurately?
[QUOTE=andypugh;1952732]... so chose one that gave me a 1:1:1 split through the threaded region. .[/QUOTE] do you mean outer tube thickness is the same as thread thickness and inner element thickness in cross sectional view?
What is outer tube O.D? Do you recall the X-axis driven nut bearings type?
Thank you for link to your CAD project - now i get the overall arrangement. By the way what do you think about fusion360? I've read i can use it for free as hobby amateur:)
Re: Harrison Universal Miller Conversion
[QUOTE=bogus105;1952830]I wonder how did you drill-out so long hydraulic pipe accurately? [/QUOTE]
I used a long drlll and trusted the existing bore to guide it.
[QUOTE]do you mean outer tube thickness is the same as thread thickness and inner element thickness in cross sectional view?[/QUOTE]
Yes. Mainly because it amused me
[QUOTE]What is outer tube O.D?[/QUOTE]
16mm I think. YOu would need to choose something to suit your machine. And might well not be able to fit the stack into the spindle drawbar bore like I could.
[QUOTE] Do you recall the X-axis driven nut bearings type?[/QUOTE]
7209
[QUOTE] By the way what do you think about fusion360? I've read i can use it for free as hobby amateur:)[/QUOTE]
It's very good, especially for the price. And you can even use it commercially as long as you make less than $100k a year.