[skip20]

This is the JET model JMD 18
http://www.medfordtools.com/Jet%20Me...orking-15.html
Any ideas on a fix for the round post!!!!!?
If the cut is deep it moves the head & lose the setup.
If I have to move the head up/down for tool change the head moves sideways & lose the setup.
Can't weld it to the post, to bad.
I have bolt the screw rack to the post top & bottom. Has helped a little but still moces sideway.
I added a AC Gearhead motor chain drive to the lift, no more cranking, just pust a botton for up/down.
This has been conv. to Stepper CNC.
Plan on build Hoss ATC setup for this.
Put 2HP DC motor with speed controller & Rev.
Has power feed when I use it in Manual
.
skip20

[bilinghm]

If only the ends of the rack are bolted down, the center can and will deflect. Drill and pin the center of the rack. Use a roll pin or a dowel.

Bill

[ataxy]

If only the ends of the rack are bolted down, the center can and will deflect. Drill and pin the center of the rack. Use a roll pin or a dowel.

Bill

i agree there is not much you can do aside that

[domonic_cnc_guy]

thats the same kind as i'm looking at getting

if you take smaller cuts you should be fine as long as those two locking bolts are done up nice and tight
if you clean the column and then lower the head onto the clean section and then do up the locking bolts at the back aparently it won't move as much if at all

[MIKE JEFFERS]

http://www.pathcom.com/~vhchan/cnc/cnc.html
have a look at this , about half way down the page rail & linear bearing
built a manual version of this works fine you may need to beef it up a bit for your application but worth a try
remember to square the colum to the table too

[skip20]

Will try the pinning idea.
Thought bout 2 - 1" Linear rails mounted to the back of the machine but haven't figured out hoe yet.
With the rack bolted down I still have play in the head assy. which is how mush it can move.
Even with the motor lift still want to move off center.
Skip20

[domonic_cnc_guy]

i would look at some kind of square rhs section with a linear bearing on it sticking out the top of the current column then you'd have to make up some kind of a mount for it to the head

[skip20]

What is rhs section?
What do you mean inside the colume?
skip20

[domonic_cnc_guy]

rhs is like pipe only square or rectangular

i'm thinking of it sticking out of the top of the mill and then make up a guide or bolt a linear slide to it and use it like an anti torsion bar

[grinderdust]

I had the head on mine move on me once while I was pocketing in some pretty tough steel. I replaced the bolts and nuts that clamp the column with grade 8 fasteners. Then a thorough coat of grease on the threads will reduce the torque required to lock the column tight. Not a single problem since. As far as locating the head after moving it, I have heard of someone using a laser pointer aimed at a far away wall with a straight vertical line drawn on it. Obviously the farther away the wall is and the more level your machine is, the better this will work. Personally, I just use a center in the chuck to locate the head to a hole of a known location while I tighten the bolts. (keeping the quill almost locked so it can't wander) This has worked for me when doing rough work (+ or - .004) and is fairly convenient because I usually need to lower the head right after all the drilling is done. If I need a closer tolerance than this, I either use an edge finder or go find some U.S. made iron! I like the ideas being put out here. Keep em' coming guys.

[aquanut]

I've just finished my conversion (key conversion anyway). I've a similar round column mill. I milled a 0.75 flat all the way down the column 180 degrees from the rack. Ground a .75x.375 cold rolled steel parallel and then drilled five counter sunk through holes for 1/4-20 socket head cap screws. Align the gound key and transfer the holes. Drill and tap the column for the five 1/4-20 bolts.

Use the flat as a guide to mark the head. Cut the key in the head. There's plenty of room in there for it. I scribed it out, then drill a bunch of holes with a .125 bit. Hack sawed the ends then knocked out the rest with a chisel and hammer. This saves a ton of file work. Do this to both top and bottom. Figure on three hours of filing by hand to get the fit just right.

Mine was belt drive, so I had to also knotch the mid pulley and sheet metal cover. I also added some adjustable "gibs" to the bottom of the head so the play can be taken out. All in all it took me a couple days to complete. I just got my angle plate in, so no chance to see how close it is.

David

[bilinghm]

[QUOTE=aquanut;408424]I've just finished my conversion (key conversion anyway). I've a similar round column mill. I milled a 0.75 flat all the way down the column 180 degrees from the rack.

Wow, that is certainly an ambitious modification. It should work our great and provide excellent repeatablity. You must have access to a large machine for the milling of the flat in the column. Cutting the keyway in the head sounds pretty challanging. Please post some pictures.

Bill

[skip20]

Pictures would be good on these great ideas.
Will be changing from 460 stepper to 39V servo in the near furture.
Skip20

[BrendaEM]

You could add a second column almost a foot behind the main column, to keep the main column from turning.

I would think that a length of drill rod, 1/2 to 3/4 inch drill rod, gliding on some drill bushings could make a fairly tight sliding situation. Brackets could be made that would be bolted on the back of the machine.

The challenge would be to make a bracket that holds the rod on the top and bottom, while the head/spindle rides in the middle of the rod. The bracket would probably have to be triangulated to make to strong against the head's tendency to rotate about the Z-axis.

The rod would have to be quite parallel with the big round column. I would think that the spindle/head would have to be ran up and down a few times to ensure this before it's final attachment.

The drill bushings are nice because they are hardened, but using flat blocks would over-constrain the head less, with a lower chance of binding it. Some kind of slotted adjustability, like milling slotted slotted screw holes in the blocks would allow them to have drift adjustability, so you can take the slack out. You would want enough contact area to take the wear, so you won't have to keep adjusting it.

It would seem that the longer the brackets are from the column centerline, the less rotational/angular slop there would be.

You might be able to figure out a way to cap-bolt the whole thing together.

[ZipSnipe]

one of our members slotted an HF round column model but I don't remember who it was. But that seemed like it worked best.

[skip20]

Using 1/8" angle, I mounted 2 roller bearing to fit the rack.
Then mounted to the top & bottom of the head.
NO LEFT OR RIGHT MOVEMENT OF HEAD.
Also have the rack bolted top & bottom & pinned in 3 places to prevent side movement.
Haven't tried it under a heavy cut as yet, but hope this fixes the headache!
Included pictures show the chain drive Power Lift I built for it a few years ago, this works great & works on AC.
You can also see the 2.5 HP DC motor I mount.
Last picture shows most of the mill.
It was CNC over 7 years ago with 460 stepper X&Y & 150 stepper on Z.
Also have a power feed on X & can still use it manual.

[BrendaEM]

Skip 20, What an elegant solution : )

[acondit]

Skip,

I second BrendaEM's comment. An elegant solution.

You could still tighten the column/head bolts to avoid movement and loosen them to raise or lower the head. I would only add a little time to the raising or lowering of the head and provide some peace of mind.

Alan

[skip20]

I do still tighten the 2 head bolt, however I changed to 2 grade 2 nuts & bolts with Grade 8.
I had to use a mig welder to add to the size of the head on the bolts to match the recess foe the head. Had to reuse the stock washers due to size but used Grade 8 nut.
I loosen the 2 bolt & boy the motor makes it easy to raise or lower the head, then tighten the bolts.
No more play in the head assy. now.