Spindle repair

Sorry, no help here, but is it just my imagination or do you get more than your fair share of grief? Or do you just have your fingers in so many pies that it's just the average amount of grief multiplied by the pies?

Can you see the end of the drawbar inside the quill? Is there maybe some so rt of snap ring inside there retaining the drawbar? Just guessing, but that 's an easy place to take a look.

Some of both. I have enough equipment something is always broke. I'm too damn cheap to buy new stuff or hire a mechanic. Also had pretty good luck getting answers here on RCM so you get to see all my life's little problems.

Karl

No

Can't see one

I'm going to try a 30 ton press on it tommorrow if I don't get another suggestion.

Karl

This may..may be of help

Some of those draw bars actually come out the bottom

Gunner

Dunno what you have for docs, but I found this at archive.org:

different from the doc I have. this is for the manual machine, mine is CNC, but it looks very similar.

It has pretty good maintenance instructions. On page 9, it just says, "remove drawbar from machine"

That gives me confidence its just stuck,bent, or something. I'll put it in the shop press tommorrow. Its soaking in Kroil all night.

Karl

pretty garbled, looks same as what Pete found.

??? Don't see how that would ever work.

Does this mean anything to you? Mine is a splined power drawbar and it surely must have a bearing in there because it rotates with almost no friction. My old series II bridgeport had this.

Karl

I just said screw it, and tossed the unit in the press. popped right out, 30 tons is persuasive.

Discovered problem, LEFT hand threads. Didn't hurt the spindle shaft, just the mild steel drawbar keeper. So, now i have a lathe fab job.

I guess left threads make sence, the spindle turns right 99.9% of the time.

Karl

How is the CNC drawbar engaged? (curious) I thought drawbars were just glorified, dual-threaded long bolts which engaged the bit from the top, drawing it into the tapered spindle hole.

Deep 7/8" impact socket and pneumatic impact wrench, Karl. Use a large diameter hose and high pressure air for maximum torque. Try it both ways to rule out left-hand threads. Maybe wedge an old bit in the collet to slow down the turning if it slips on you.

Keep in mind that they lift to tighten and many have a fairly big tool knob retaining gizmo on the end of them. So in many machines..they ONLY come out the bottom. That knob on the end of the draw bar often times ...unscrews. The Moog/Visimetrics only come out the bottom as do a number of others.

Ayup!

...

power drawbars have splined ends with points on the end of the splines. There's a female mating spline on an electric impact wrench and an air cylinder to drop it in place.

Wish I'd ask you BEFORE I broke it :)

Karl

Old style power drawbars on CNC or even manual mills just drive a regular threaded drawbar with an impact wrench. Modern CNC drawbars have a collet on the end that grabs a pull stud on the tool holder, and the retaining force is provided by a stack of belville spring washers. The release force is provided by a hydraulic cylinder.

OK, that covers the top end, but what about the bottom? Are the bit adapters tapered and do they have threaded tops like their manual counterparts? I don't yet grok the mating method, -especially- after seeing the spindle parts you showed. I only saw female bottoms, if you will. (quiet, Mikey. ;)

I'm glad to share my vast (2+ hours) experience on milling machines with you.

Look for the round gizmo sticking out of the top end of the tool holder.

And a slightly different type

This is a pull stud that gets screwed into the end of a tool holder

So there's a grasping mechanism in the spindle which grabs that button? Or levers to wedge it upwards, seating the tapers together? Got any photos of cutaways or exploded diagrams? They're always easiest on my grokker.

Greetings Karl, I have an old Index mill that uses the same type of power drawbar. Even though the splined ends are pointed they would sometimes not engage the female spline proiperly and the impact wrench would just spin while trying to knock off the points on the ends of the spline. So I installed a switch in the common wire to the impact wrench that would only close when the splines were mated properly. Since then the power drawbar setup works very well. Eric

It's an ordinary threaded drawbar - a long glorified bolt. The only difference is that it is driven by an impact wrench instead of manually with a hand wrench. Pretty much all the older CNC adaptations of manual mills were like this, and those power drawbars were also used on manual mills that were large enough to be a pain to reach the drawbar manually.

Modern CNC machines use a drawbar with a collet that grabs a pull stud on the tool holder. No rotation, just linear action. The retention force comes from a stack of belville spring washers on the drawbar. A hydraulic actuator pushes the drawbar down compressing the spring washers and allowing the collet to release the pull stud.