trlvn's terrific travelling RF30 tale

[trlvn]

Did you give consideration to putting casters on the stand? Would allow you to move it around if need be.

I'm really hoping that I won't need to move it very often or very far. Basically just need to slide it a few inches from time to time. Also, casters would raise the height of the machine even more.

At one point, I thought about replacing the stand with the cabinet that Busybee currently sells ($300). The main reason would be to get more usable storage space under the machine. I decided that it wasn't a big-enough upgrade to justify the cost.

Craig

 

[trlvn]

Good job on the long awaited move. My machine is like YYCHM's with the column and upright being together, Mine is a LC-30A not a RF30, came from a different part of the empire i guess.

The way I thought I understood it was that Rong Fu developed the original design and then a bunch of foundries/factories over there basically copied the machine. Apparently some are very similar and others less.

Craig

 

[trlvn]

On the stripped bolt problem, the plot took a minor twist.

First, there are undamaged threads in the lower section of the problem hole. Just about 1/2 inch seems to be in good shape. Normally, I would think that is fine--a 7/16-14 nut has less than 1/2 inch of thread, after all. But, ALL the holes are quite a sloppy fit for the bolts. The following is a link to a very short movie (on Microsoft OneDrive) showing what I mean:

loose bolts.mov

MOV File

1drv.ms

I'm going to replace the bolts with longer ones but they don't seem to be the problem. At most, they seem to be only 7-8 thous under the nominal size (0.4375). Are Grade 5 or Grade 8 bolts made to a tighter standard?

Drilling out all 4 to install helicoils seems like overkill. Changing to 1/2 inch socket head cap screws would be less expensive and at least as good a physical connection. Since there is 1 inch of casting to thread into, I would think 1/2-13 (UNC) would have lots of holding power. Sound right?

Incidentally, Bubba used flat washers but the parts diagram calls out spring washers. If I go with socket head cap screws, I would lean towards flat washers to spread the load slightly. Any thoughts on this?

Just to be clear, this is the connection where I'll be adding any shims to tram the head. I have never trammed this machine as it was always intended to move it to the basement. However, there were no obvious problems when I was using it in the garage. Even though only 3 of the 4 bolts were holding the head on!

Craig

 

[Susquatch]

I don't normally find any difference in class fit between regular, grade 5, and grade 8. However, you can buy Bolts with a higher class fit. If you have a lathe, you can also make Bolts with a perfect fit. Nobody says they need to meet regular standards.

My advice is different. If I were you, I would drill out the thread and put helicoils in. This fix is good as new, uses the original bolt, and whoever gets your mill when you are gone will never know the difference.

Coned (Belleville spring) washers are designed to impart a prevailing torque even when the part connection shrinks a bit. This can be important in prestressed connections that move a lot. I could see that being the case on a mill column that is working hard and chattering away. If that was the original design, I would not replace them with flat washers without doing a design analysis first. Keep in mind that spring washers are very seldom used to accommodate the bolt strength, they are used to accommodate the part strength and movement. In other words, switching to a higher grade bolt will not help and may actually hurt. I say all this with ZERO experience with your mill, but a crap load of experience with fasteners.

Coned washers are readily available so why mess with it.

 

[John Conroy]

If you are going up to 1/2" bolts it would be better to use 1/2-20 fine thread as the correct drill size is .453. For 1/2-13 the drill size is .422 and the holes won't completely clean out the old threads.

 

[trlvn]

I don't normally find any difference in class fit between regular, grade 5, and grade 8. However, you can buy Bolts with a higher class fit. If you have a lathe, you can also make Bolts with a perfect fit. Nobody says they need to meet regular standards.

My advice is different. If I were you, I would drill out the thread and put helicoils in. This fix is good as new, uses the original bolt, and whoever gets your mill when you are gone will never know the difference.

Coned (Belleville spring) washers are designed to impart a prevailing torque even when the part connection shrinks a bit. This can be important in prestressed connections that move a lot. I could see that being the case on a mill column that is working hard and chattering away. If that was the original design, I would not replace them with flat washers without doing a design analysis first. Keep in mind that spring washers are very seldom used to accommodate the bolt strength, they are used to accommodate the part strength and movement. In other words, switching to a higher grade bolt will not help and may actually hurt. I say all this with ZERO experience with your mill, but a crap load of experience with fasteners.

Coned washers are readily available so why mess with it.

Hmm, I was interpreting "spring washer" as a split washer or lock washer. IE to prevent the bolt backing out due to vibration. There is not enough detail in the diagram to see exactly what they mean. It's a 'Chinglish' document so there is a good chance they haven't used a precise technical term.

On your mill/drill, what sort of washer, if any, is on the bolts that connect the column to the base?

Craig

 

[trlvn]

If you are going up to 1/2" bolts it would be better to use 1/2-20 fine thread as the correct drill size is .453. For 1/2-13 the drill size is .422 and the holes won't completely clean out the old threads.

Thank you -- excellent point!

Craig

 

[Susquatch]

Drilling out all 4 to install helicoils seems like overkill. Changing to 1/2 inch socket head cap screws would be less expensive and at least as good a physical connection.

I watched your video. It doesn't scare me at all. Bolted connections are designed to stretch a bit and threads have a 60 degree conical profile to allow that to happen. Your movement looks typical of what I would expect to see in a nice clean setup.

I certainly don't think you need new bigger Bolts. Just fix the one damaged hole with a couple of helicoils and be done with it.

One more thought. What you might think is loose, might actually be intentional. Especially when you know the oem connection used spring washers....... The whole assembly might be designed to absorb vibrations (cyclic stress & strain) without moving and without failing in fatigue.

 

[Susquatch]

Hmm, I was interpreting "spring washer" as a split washer or lock washer

Excellent point. Which is it?

 

[historicalarms]

Congrats on the move Trivn ....but I must make a point that concerns me to no end....your bench.

Personally I think your leg stance is so narrow as to be dangerous with a big mill-drill. On a mill-drill, head rotation is possible in a 360 deg circle and you might not plan on ever rotating 180 deg's but if you do with that leg stance the possibility of the heavy head overhang counterbalancing the whole machine into a crash to the ground. The warehouse foreman where i bought mine was very emphatic for me to make my bench stance wider than the circumference of head circle and BOLT THE BASE DOWN...his words " every machine we get back for repair has fell over sideways from overbalancing".

Make your floor contact wider than the head swivel radi.. In your case a simple fix with a 1/2" x2" flat bar longer than any sideways overbalance possibility welded to the feet will do the trick.

 

[CalgaryPT]

@trlvn Yup, and that is what I have done. But it is not getting any easier on my knees. Right now I've got a baby food jar of oil and a solder brush that I use to 'paint' on some oil.

LOL. The way this is written makes you sound like the Tin Man, oiling up your joints to make it through the day.

No disrespect intended of course, as I am right there with you. Personally I am thinking of putting zerks in my own knees.

 

[trlvn]

I watched your video. It doesn't scare me at all. Bolted connections are designed to stretch a bit and threads have a 60 degree conical profile to allow that to happen. Your movement looks typical of what I would expect to see in a nice clean setup.

I certainly don't think you need new bigger Bolts. Just fix the one damaged hole with a couple of helicoils and be done with it.

One more thought. What you might think is loose, might actually be intentional. Especially when you know the oem connection used spring washers....... The whole assembly might be designed to absorb vibrations (cyclic stress & strain) without moving and without failing in fatigue.

Interesting! Being that it was made in China, I was leaning towards sloppy manufacturing rather than rational and intentional design. As I noted, it seemed to work OK with just 3 solidly connected bolts. BTW, the stripped one is to the operator side. All the static load would be on the fasteners on the other side. Dynamic stresses would basically have to overcome the weight of the head before putting much load on the front-side fasteners, no?

OTOH, I've checked the column connection and the holes in it are already big enough to accept 1/2" bolts. I was concerned about space but, checking now, I think there is room for a hex bolt head and wrench. I've got the 1/2-20 tap (4 of them, actually--gotta love auction box lots) and the tap drill. I'm leaning towards up-sizing the fasteners.

I have a little bit of trepidation because either with a helicoil or upsizing to 1/2-20, I'm going to have to drill the holes freehand. (29/64" in either case.) I'm sure it will go fine (famous last words) but I really have one shot at this. If something crazy goes wrong, say like a casting flaw, then it is going to be much harder to fix.

Craig

 

[trlvn]

Excellent point. Which is it?

That's why I asked you about what washers are on your machine! Bubba has already been messing with mine so I don't know how it came from the factory and the poor docs I have are unclear.

Craig

 

[trlvn]

Congrats on the move Trivn ....but I must make a point that concerns me to no end....your bench.

Personally I think your leg stance is so narrow as to be dangerous with a big mill-drill. On a mill-drill, head rotation is possible in a 360 deg circle and you might not plan on ever rotating 180 deg's but if you do with that leg stance the possibility of the heavy head overhang counterbalancing the whole machine into a crash to the ground. The warehouse foreman where i bought mine was very emphatic for me to make my bench stance wider than the circumference of head circle and BOLT THE BASE DOWN...his words " every machine we get back for repair has fell over sideways from overbalancing".

Make your floor contact wider than the head swivel radi.. In your case a simple fix with a 1/2" x2" flat bar longer than any sideways overbalance possibility welded to the feet will do the trick.

I think maybe my picture is making it look worse than it is. The legs splay a bit and the feet cover about 22.5 inches left to right. The spindle is about 10 inches from the column, centre to centre. So the spindle centre is just inside the feet. I have never rotated the head straight back. In that case, the spindle would be beyond the feet. Whether the mass of the stand and base would be enough to keep it upright, I don't know. I'll certainly be careful if I ever find a need to do that.

Craig

 

[Susquatch]

That's why I asked you about what washers are on your machine! Bubba has already been messing with mine so I don't know how it came from the factory and the poor docs I have are unclear.

Craig

Sorry Craig, I didn't realize that you were asking me. Mine is certainly very similar. I will look when I get back to the shop.

 

[Susquatch]

I think maybe my picture is making it look worse than it is. The legs splay a bit and the feet cover about 22.5 inches left to right. The spindle is about 10 inches from the column, centre to centre. So the spindle centre is just inside the feet. I have never rotated the head straight back. In that case, the spindle would be beyond the feet. Whether the mass of the stand and base would be enough to keep it upright, I don't know. I'll certainly be careful if I ever find a need to do that.
Craig

IMHO, I think you and @historicalarms are both thinking heads when the issue is really probably something huge on the table. Farmers like me put humungous things up there to work on. I have been postponing a job on a Ripper tooth that I know for sure weighs more than that head. Two big men can barely move it a few inches. I had planned to put the bolted end up on the side of my mill table with an engine hoist and then slide it to center. But after reading all this, I will probably try to figure out how to center load it instead.

 

[Susquatch]

Interesting! Being that it was made in China, I was leaning towards sloppy manufacturing rather than rational and intentional design. As I noted, it seemed to work OK with just 3 solidly connected bolts. BTW, the stripped one is to the operator side. All the static load would be on the fasteners on the other side. Dynamic stresses would basically have to overcome the weight of the head before putting much load on the front-side fasteners, no?

Not necessarily. If you stop thinking about overload stress failure and think instead about fatigue from cycles, an excessively loose front fastener can fail. Since you don't have the original failed bolt, you will never know for sure, but it is possible to check for other evidence. A stress analysis would require modelling and strain gages - which are more work than its worth. If it were me, I'd just duplicate whatever the factory did.

A few comments. I bet that head weight can be easily lifted by the quill crank. How much down force was being applied by the previous owner?

Cyclic stress and strain does not need to lift the head to fail the bolt. A front bolt could fail from fatigue without ever being overloaded.

I have no idea what the design limits were. Nor could anyone but the designers themselves. I am only pointing out that the whole situation might not be so simple.

I'll give you a classic example. Have you ever seen a failed wheel stud on a car or truck? They happen all the time. Most people assume that some gorilla over torqued the bolt and it snapped a few days later or maybe going around a corner. This is NEVER the case. It is ALWAYS the result of undertightening. The nut or bolt will always strip before it breaks from overtorquing. And it will almost always snap in fatigue failure if it is under torqued.

Anyway, it is not very hard for me to imagine an excessively loose bolt failing on a mill that does so much bouncing as it cuts. This was actually one of my hates about my mill drill. It was never very solid or rigid compared to either of my big knee mills. I've had that thing bouncing around like a male rabbit way more often than I should have.

So before everyone piles on, be gentle - I'm old. These are all just pure conjecture on my part noodling the possibilities on something I have not seen in person.

My best guess is still the gorilla on the wrench overtorquing a steel fastener in a cast-iron hole. But that is just my best guess.

In all reality, I'm still on the page of installing a few helicoils only in the failed location, use original size and grade of fasteners, and torque to specifications - no more no less. Drilling, tapping, and installing helicoils is pretty easy to do with hand tools because everything follows the existing hole and the existing threads.

I'll head out to the barn shortly and I'll let you know what is on mine. I'll also do a little noodling on the what-ifs while I'm looking at it.

FWIW, I've learned that @RobinHood is pretty good at forensic failure analysis. If I were you, I'd be interested in his opinion on this one too.

 

[6.5 Fan]

I'm wondering if those bolts were originally metric? My LC-30 has metric fasteners.

 

[Tom O]

It would be interesting to see the measurements of the bolts using the wire system just to see what they measure have you tried a tap in the hole to see how it fits?
Busy Bee’s base does have the little cabinet in it but I seldom use it other than storing the toolbox it came with.

 

[Susquatch]

On your mill/drill, what sort of washer, if any, is on the bolts that connect the column to the base?

Mine has no washers at all. The Bolts on mine are all Grade 8 1/2-13 x 1.5" Socket Head Machine Screws. They look original. I have no idea at all why they were used in this application. Grade 8 Bolts into regular old cast iron doesn't make sense to me. Sorry about that..... Maybe a previous owner upgraded the bolts thinking stronger is always better???? Or maybe the clone boys wherever they are thought that too?

On close inspection, and assuming yours is similar enough to mine, I am still solidly on my original guess and MUCH LESS inclined to think yours failed by fatigue. I simply think yours was over torqued by a gorilla and the threads in the base were pulled out. Normally, the bolt would strip first, but a grade 8 bolt (if that's what yours had too) would strip the casting long before the bolt.

If I were you, I would not get too worried about hand drilling and tapping for a heli-coil. Just do it and be as careful as you can. You have the post to help you see that the drill is at the right angle and you have a hole that is already there to follow too.

Proper torque for a 1/2-13 fastener into cast iron is a numbers game that I have forgotten how to do long ago. As I recall, the strain of both halves should be balanced against each other and the set point selected according to weakest material. To do it right, it would have to done in a lab because cast iron varies considerably. The torque has to be derated to factor in the precise strength of the particular grade of cast iron. I'd love to know what your manual says it should be so I can record that for mine. In the absense of that, I'd probably go with half the torque (instead of 60%) of a regular 1/2-13 bolt. Roughly 30ft-lbs. Then I'd mark the bolt head and watch for movement. If it moved, I'd prolly put regular loctite into it. Or maybe just go with loctite regardless.

Depending on the quality of the casting and the material composition, fine threads are not normally recommended in cast iron. Most bolted connections are designed to be torqued at around 60% of the tensile strength of the bolt material. This ensures enough stretch to stop the bolt from turning without over stressing the bolt. The nut gets ignored because it is a bigger diameter than the bolt and won't usually fail. For similar materials (eg bolt and nut the same) this is easy. But when the nut (casting in this case) is a different material, this approach goes to hell in a handbasket. For threads in cast iron that don't follow a normal steel stress/strain curve, course threads are better than fine. Basically, the stretching bolt shears off the casting threads one at a time as it stretches and the casting doesn't. Fine threads break off this way easier than course ones do. If the cast iron stretched or compressed the same as the steel, this wouldn't be an issue.

I don't really think all that was any help to you, but too much info is better than not enough.

Again, helicoils, loctite, original bolts, 30 ft-lbs. Best I can do without better info. If you really want to go with bigger bolts that's probably fine (assuming the ears don't get too weak), but in cast iron, I'd stick with course threads.