New Machine Build- Jet 830 CNC Retrofit

[Adamj12b]

Hello Everyone, I am starting this thread about my latest CNC retrofit adventure with my father-in-law of our Jet JVM 830 knee mill. We picked it up off a guy for 200 bucks. Date on it is 1978 and it looks like it. All of the screws are very sloppy and will hardly cut anything because the spindle bearings are so worn out.

We have already started work, and will bring you up to speed.

I started with dismantling the top half of the machine and taking out all the spindle and quill relate parts. After a good cleaning, I took all the parts that Had paint on them outside and pressure washed them, removing any lose paint and grime. I then dried them off and let them sit in the sun for a few hours. Later that day I went pack and painted them with Rust-Oleum Almond
Semi Gloss. It is almost the same color as the new Jet equipment. While I was doing this he cleaned the rest of the base of the mill and painted that as well.

I ordered new bearings for the spindle and idler pulley from VXB.com, and installed those. When the machine was set up before for its max speed, it would make this awful "Whirring" noise when running. Thats at 3440 RPM. Now, with the new bearing it is almost totally quiet when running at that speed. We have not tried cutting anything, because we have removed the table and screws so that the screws and nuts can be replaced.

For screws and nuts, We went with Roton 1x.250 inch screws and single recirculating square ball nuts. We only went with single nuts, mostly because of budget. I am in the process of machining the ends of them down to match the stock ones right now. I am almost done with the Y and the X is already complete.

We have also replaced the bearings that support the screws. These I got at my local NAPA store.

During all this work we have also been planing out all the cnc stuff. He got an electrical box that measures 20x18x7, and has a hinged door and a removable panel inside for mount the components on. This will house the motor drivers, power supply, breakout boards, relays, contactors, a VFD, and anything else electrical that is needed. He mounted this box the the side of the mill with 4 bolts and a few holes that were already there. The top of the box had to be space out 3/4" from the column, because it is slanted inwards at the top, and I wanted the box to be straight. I also added a 115VAC 110mm fan to the box to provide cooling for all of the components.

On the top of the box we built an arm to mount an LCD monitor for running the machine. This consists of a electrical meter hub connector, an emt conduit pipe fitting, a 90 degree piece of 1-1/4" emt conduit and a 6 inch piece of 1 inch angle iron. The hub was mounted to the top of the box and the fitting screwed into it. The angle was welded to the end of the 90 and the monitor attached to it with some hinges that were already on it. The other end of the 90 is inserted into the fitting and the fitting is hand tightened. This provides a study mount for the monitor, while allowing it to be tilted up and down for easier viewing as well as being rotated out of the way when the machine is not being used.

For motors we are planing of using these: Servo

For a power supply we are planing on using this transformer: Transformer

We will be using G320 gecko drives to control the motors and a CNC4PC BOB.


Well I think that is all for now, I will try to keep this updated as progress is made. I am open to suggestion to hope some of you have some for me. -Adam

Picture 1+2: Machine after we got it, before starting work on it. Thats what it looked like when we got it.

Picture 3: Spindle and head parts on bench

Picture 4+5+6: New paint, Spindle installed and electrical box with monitor.

[Adamj12b]

Its been awile since I updated where were at with the mill, so here I go.

We have finished the X axis ball nut mount and it works perfectly. We were able to tighten down the gibb so that with the nut not installed it is really hard to slide the saddle, but with it installed it takes no effort at all to make it move. Were very happy with it.

We have also been working on the Y axis screw but it has been very hard going. No matter how hard we try and how careful we are the screw wobbles when it is installed in the bearings. Were working on welding a shoulder on to the end near the bearings to try and help the problem.

We have mounted most of the electronics in the enclosure, including the heat-sink for the geckos, the transformer, rectifier, cap, and the contactors and relays. We added a fan and some air intake ports to the enclosure also. As kind of a novelty thing, we put the fan on a thermostat to regulate the temperature inside the enclosure. The shop is not heated all the time, so in the winter it will be cold, so the electronics will keep themselves warm instead of cooling off even more. In the summer the fan will run keeping them cool.

The computer as been hooked temporarily up to a C10 bob which controls a solid state relay, which controls the spindle contractor. This board is going to be replaced with a C11T and the C10 will just be used for extra inputs. For main power we ran a new 30 Amp circuit to the machine and got a 4 pin dryer plug and outlet. This cord goes into the enclosure and into the main power contactor. From the main contactor it gets dispersed out to the spindle contactor, and other parts that need power.

We received the 3 servo motors on friday the 11 and were very surprised that how big they actually were. The picture looked like they were big, but theses things are huge.

We also got our encoders on the friday as well. They are 1024 line ball-bearing mounted encoders that are sealed. They were 15 bucks a piece and the guy threw in a fifth one for free!

We decided to mount round weatherproof electrical boxes to the back of the motors to house the wiring connections and the encoders. This will allow us to use 1/2" seal-tight connectors with 3/8" seal-tight for conduit for the wires.

We fabricated both the X and Y motor mount brackets last weekend, and finished the Z this weekend. For the X and Y we used 3/8" aluminum sheet and cut the brackets out from stencils that I made with solid-works. They were cut with mostly a chop saw, table saw and a band saw. They were cleaned up with a drum sander and files, then textures and smoothed out with an orbital sander. The Z axis mount was made from a piece of 1/4" aluminum sheet, a piece of steel angle, and a piece of 1/2" steel bar. We simply mounted the aluminum inside the knee inline with the knee screw, and mounted it with the 2 pieces of steel. It is very rigid and will work great.

As for pulleys, we bought 3, 40 tooth size L (3/8" pitch) 3/4" wide steel pulleys with double flanges and 3 10 tooth 3/4" wide aluminum pulleys from econobelt.com. The 40 tooth ones came with 5/8" ID holes which worked fine for the X and Y, But I had to bore out the Z pulley to .7874" or 20mm to fit the stock screw in the machine. I did this with a 3/4" drill bringing it to .750" then using a boring bar, I brought it out to the final ID. All 3 of the small 10 tooth pulleys had to be drilled out 5/8" to fit on the motor shafts. This was also done with my lathe. These were just chucked, checked with a dial indicator to be centered and then drilled with a 5/8" drill bit.

I will leave off here with some pictures. I will be posting some videos tonight, for I will be installing the belts and applying power to the motors to see it move. -Adam


Picture 1: New Cabinet Door Seal
Picture 2: X axis Ball Nut Mount.
Picture 3: Enclosure fan, 30 amp dryer plug, and seal-tight to motor
Picture 4: Rectifier and cap with spindle contactor
Picture 5: Electrical Box with panel installed
Picture 6: Motors and Encoders next to med. Mc Donald's Cup
Picture 7: 1024 Line Encoder
Picture 8: Y Axis Motor Mount
Picture 9: All Six Pulleys

[pete from TN]

Hey man I was enjoying your build of the knee mill. I am looking at a used Grizzly G1008 that is in very good shape and I may get it. They look like a decent rigid machine for the size and money. How do you like your machine and do you feel it is a good one for the conversion? are you planning on doing the knee or the quill for the drivez? appreciate it and peace....

[Meganick]

What kind of accuracy and backlash are you seeing on the Roton ball leads screws/nut? What part number did you order? Not seeing accuracy data called out on the Roton site.

Surplus Center Servo link has gone stale. Any info on current equivalents?

Nice looking machine!

[Adamj12b]

Thank you. The Screws, I later found out, are not meant for this application. They are designed for a linear motion setup, not positioning. But the results are not that bad. I only have a few thousands backlash (.003), but that was right after I built the machine. I have not checked it lately, as I have been very busy. That is why it has taken me so long to respond.

As for part numbers: http://www.roton.com/Mating_Componen...mber=59305&#PN

That is the page with the screws and nuts. I only used a single return square nut on both axis's. If i were to do it again though, I think I would spend the extra and get some Nook or Thompson screws. I didn't want to spend too much on this machine though. It is 30 years old, and it has seen alot of use, and abuse. So I didn't see the point in spending many time what i paid for the machine($200) on just screws.

As for servos... I wouldn't really recommend the ametek servos for a mill of this size. While the X and Y axis's are ok, the Z is very underpowered for the knee. I spent some time on the phone with Mariss form gecko drive and doing the math, he came to the conclusion that the motors were less then 1/10 horse power. Basically, you can get more power out a NEMA 23 stepper motor. LOL.

But for matching servos, check out http://www.kelinginc.net/ServoMotor.html

There 600 oz-in NEMA 34 servos is close to the ones I have, but it is much more powerful.

I also did the Quill with a geared stepper motor. With this Im able to move the quill up and down at 120 IPM! It is very fast. But, there is only about 3 inchs of travle in the quill, so it dosent really help on larger parts. But on small parts it speeds up work time alot.

I hope this helps.

[pete from TN]

Well it seems to me that if you are getting around .003 or so on backlash without the aid of a zero backlash nut assembly then you are doing pretty good. I have purchased the same screws for my Lathemaster mill conversion and I have two nuts in a preloaded zero backlash assembly and I hope that it will take out any excess backlash but time will tell. I know most that have built their machines try to either buy a preloaded nut or make one with two nuts to accomplish the same thing. There are several different designs on the net for accomplishing this that take up little room and are homebuilt. I just got the Grizzly knee mill here recently and I am quite pleased with it. It is noticeably more rigid than even my Lathemaster mill which is pretty stout for a bench mill. I am half tempted to convert it instead but I already have the Lathemaster torn down and started the conversion. Perhaps I will like it so much that I will do both of them in time. Anyways, I enjoyed your post and would love to see more pics and maybe a video of the machine and some parts you made with it....peace

[Adamj12b]

I will get the exact numbers for you tomorrow. They vary between each axis. I will also get up another post with some more pics to update my progress. There are some videos on youtube also. http://www.youtube.com/user/Adamj12b

Ill get back soon.

-Adam

[Meganick]

Pete - what Grizzly knee mill did you get?

Adam - while you are at it, any way you could also make a guess at how accurate the Roton ball screws are? I am not pleased with how rough my Thompson rolled screws are running on my RF-30 and am looking for alternatives.

[OT-CNC]

Nice job Adam! I'm currently retrofitting an old JET jvm-626 model. It looks a little like your mill, just a bit smaller. I'll post some pics once the z-axis is done. What are you doing about lube on your mill? I found that mine had a few "blind" oil ports. I had to drill the gibbs to allow for oil passage to the ways LOL. I ended up installing a Bjur central oiler which works nicely.

-OT

[pete from TN]

I have had it for a short time now but the machining I have done on it makes me feel very good about my purchase. I am really surprised at how rigid and quiet this little mill is and I can use some pretty gnarly big endmills to cut on it with no drama. I got some rougher endmills with it and I have never used one but man are they nice and remove material with authority. This mill came with an x axis power feed unit as well as a bijur type oiler setup and the movements are real nice and tight. I was able to use a 1/8 inch endmill to cut a rather deep slot in a receiver I was machining and it cut perfectly and left a very nice finish, something I have not been able to reproduce on the bench mills I have here. The belt drive seems to have some serious speed too compared to the other mills I have run. That little 1/8 inch mill was screaming and cut real nice. The size of this machine is probably ideal for a hobbyist/ home machinist as it does not take up too much room but it has the kind of rigidity normally found in much larger machines. I had to remove the millhead to transport it and that thing is VERY heavy and took three guys to lift onto the column. The machine also has a splash tray integral and a sump with pump to allow coolant flow altho the pump looked to have seen better days when I took it out to clean the machine. I will either try to fix it or just get another pond pump and rig it up in there because I have had good luck with my setup for my bandsaw that same way. If you guys know anyone looking for a cheap mill I am now gonna sell my Rong FU RF30 mill drill with power feed on the x and factory stand to make room and help repay the bank with for the new mill. I am in Tennessee on the east side....peace...

[Adamj12b]

Sorry its been so long. Ive been really busy buying and fixing up my first house.

About the backlash. I cant remember exactly, but the X has about .004 and the Y has about .006. As for the Z....that has like .025 on it. Its just the stock Acme screw and its obviously worn badly. Once the house is done, I will be replacing it with a ball screw.

As for oil. For now I am just doing it by hand. The machine originally had some holes and channels that someone added, all connected to tubing and then an oiler, but the hoses broke and need replacing. That is on the TO DO list as well.

I also had a chance to fit The X and Y servos with 16 tooth timing pulleys. Up from 10. With these I am able to get 65IPM rapids. I have also cut some test pieces in Oak and Ash at 40IPM. Works great, But thats about all its got because the spindle only turns 3223 RPM. Once the VFD and new motor get bought and installed it should be able to handle the high speed. Even traveling at 65 IPM, it dosent have any trouble with force.

I got the quill drive working also. It is able to rapid at 120 IPM. It really cool to watch it do a 3D job with the quill going up and down quickly. The E-Stop is also all set. So is the Spindle tach sensor. Im still working on buttoning up the electrical cabinet. Im going to be replacing the encoders with some lower power once, because right now I have to power them from a separate power supply for each as to not overload the geckos.

Here are some pics.

[OT-CNC]

Adam, you may be able to dial out more of the backlash on the Z. The way you have, it's basically a rack and pinion. If you can adjust the bearing caps towards the quill, you can increase the gear contact and thus reduce the backlash.
I'll be following your updates, I'm interested in your VFD and motor upgrade.

-OT