Knee mill XZ7550C CNC conversion
Hi to all you guys and girls!
I have just bought this mill and plane to convert it to CNC. The mill looks fine the price was right and it seems to me that it has a good potential for a solid cnc conversion. I have looked all over for similar machine and found that it is selling all over by different names.
This one came from China (like every thing else) and it is being sold here in by the name ALFA XZ7550C . In other places it is being sold by different names like, Stealmaster in Australia and Knuth in Germany. All do I spent considerable amount of time searching for a CNC conversion attempt on this machine I have fount nothing And if any of you guys have any knowledge of any attempts of similar mill conversion please let me know I would love to see what problems can I expect further down the road.
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As it was difficult to move the mill in one piece I had to dissemble it and bring it piece by piece to its final location. Looking at the castings they are as expected for a low budget machine but that dose not concern me as much as the period that they have been cured.
That aside the machine seems rigid enough for my needs. And I did not find any faults in the rail slides like porosity of the casting all in all so far so good.
Another pic of the knee assembly, heavy as hell for a two person team. The column is just under 200 kg.Good thing I had a good breakfast that morning.
Just so you know, there is at least on person watching this thread with great interest.
Thanks for your support really appreciate that.
Ok progress , progress.
Today I goth around doing something useful I have inspected the castings and rails and goth the z axis ball screw in place (almost) , check out the photos.
I get the Chinese quality and I knew what i was getting my self in to but it wouldn't hurt if they gave it just a bit more love ...
BONDO BONDO , It is amazing how much bondo can you fit on a mill.
OK enough badmouthing my mill !
Now for the god things.
This old screw got to go.
And this (almost) new grounded precise preloaded ball screw that I goth of of my friend is going in.
I had to have it machined so it can be fitted exactly ,and yes that is a chain sprocket.
Usually I would newer put a chain drive to a CNC machine but this is a bit different.
First I had it laying around ,second it is not any old bicycle sprocket NO NO . This is my left over racing bike cam chain from my Yamaha r1.
Ok this is what it looks like and this sprocket goes on the motor , I just need to make it fit to the motor shaft. Chain looks like it is made for the job and I am convinced it will do it wery well, and it will be a direct drive ill explain later why.
I even goth around making a mounting flange for the ball screw .
just need to drill the holes and it is done
I am not sure what is the proper English name for this little pin but I made that too so the mill will have bevel gear mounted to the ball screw as well so that I can run it in a manual mode over the handle bar.
Test fit , and yes ,looking good , and it feels very smooth turning it by hand.
This is the place for the motor , it should fit nicely just under the table but as I don't have any flat surface to mount it on ill have figure out what to do and how to machine the motor mount.
Vices for the mill.
I am assuming you have seen this thread ... Hafco Metal Master HM-52 CNC Conversion.
I think the mill that you have and the HM-52 are quite similar other than the HM-52 also has a horizontal spindle and the XZ7550C does not. The HM-50 without the horizontal spindle would be identical to yours I think.
I have the same mill I converted to cnc. Things to be aware of, completly strip the spindle and remove the powdery grease and replace with decent spindle grease, about a week after I got mine I needed to do a job where the spindle had to be run CCW and after 5min the spindle started to bog down. I stopped the spindle and found it really stiff to turn. After stripping down I found dried crumbly grease around the taper bearing.
Most of the small screws eventually get loose as the internal threads seem oversize so I used loctite a fair bit.
I also followed the Hafco mill thread and used a 4" cylinder to take the weight of the knee which has worked very well.
I also fitted a pressure feed oiler system to all the ways and ballscrews as these ways are not hardened and will wear pretty quick if not kept lubricated. As I havn't had the chance to completly strip the mill as you have I would have liked to cut some oil grooves in the ways but they always seem to be pretty wet.
Things I haven't sussed out yet is the noisy gearbox or is that normal?
Also the head pivot seems a little weak, I have a problem where if I put a dial gauge between the table and head body and with mild hand force on the top of the gearbox I can get 0.1mm of springy movement. I've tightened the 3 holding nuts with an open ended spanner until the jaws started spreading (there is no room to get a ring spanner on them) . So if at some time you check the mating surfaces for flatness around this area I'd be interested in what you find.
Good luck with your build.
Did you have to cut away as much material as he did to get the cylinder to fit? Anything that you did different to install the cylinder?Originally Posted by cjmerlincnc
Hi, No i didn't cut anything away, it's been a few years now but if i remember all i did was to grind away some crud under the knee. I mounted the cylinder in the same position to the hafco thread but on top of the base unit. This meant I had to lose some travel on the z at the bottom but since using it I havn't had any problems fitting stuff on the table.
My, my it has been a busy week! Now that holidays are over I am ready to get this project going. So lets get on it!
Thanks for that thread it is awesome, and that machine is similar to mine I would say that it is the same manufacture in china and they just changed the name.g , other thing is the flexing problems which I found to be allover the machine. I would love to have servos like that but I am on a budget which is very tight. I have noticed that I have similar issues whit my machine, like whit the spindle for example which has quite a big run out ill have to disassemble the quill and check out what is wrong , but that I'm gonna deal whit that later now I need to get it to work ASAP.
The spindle problem seems to be generic to those machines soon as I finish whit the conversion ill get the spindle down and check it out and replace the gears whit the belt drive and I have my eye on a bigger motor because I am aiming for 6000 rpm at least.
I have a similar way to neutralize the load on a knee but lii do that whit smaller pistons like the ones for the car bonnet support.
My mill has grows in the ways I suppose that they added them in later versions.
I checked the tilting head mating surfaces and they seem fine but there is a loth of flex on the machine and ill make some pictures later on to demonstrate the problems I found.
Ok, Z axsis balcsrew mount finished and screwed in place.
These are the motors that I will be using, this one is for the z axis and that is the gear mounted on and ready for instal. Motors are nema 34 1600oz from wantai. I am runing them on 60VDC. I made some test runs whit mach and it seems that I cant get them faster than 200-300 rpm so ill be running all of them on direct drive and hope it will run ok. I don't have any experience whit this particular model so if any of you guys would let me in on the hidden details I would appreciate it. I would Lowe to have some servos but that will have to wait for now.
This is the motor on test run whit small nema 23 425oz beside
And by the way this is an touch screen that I had laying around and it is perfect for this project
Last edited by mars051; 04-01-2013 at 05:37 PM.
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