Freeing a Welded (Spun) Head
Here's a long and detailed thread about the various approaches that may work when a cutterhead has been welded to a spindle. February 15, 2009
Question
I have managed to weld a high speed steel head to my horizontal spindle. I've done this before with an aluminum head. I just took a gear puller and pulled it off. This steel head isn't budging. I am open to suggestions and am in trouble without the ability to run my molder.
Forum Responses
(Solid Wood Machining Forum)
From contributor C:
If all else fails, heat the head with a torch, very carefully, and the head will expand faster than the spindle. Put pressure on it with the gear puller while you are heating it.
From contributor C:
My suggestion presupposes that the head is not really welded to the spindle, but that it has been on so long that it is corroded or sweated to the spindle. If the head has spun on the spindle and either of them have changed color due to the heat generated, then it is really welded and both are ruined.
From contributor W:
If you’re getting serious, then get a large heavy duty gear puller and crank it all the way tight. Then with a good size hammer smack the back bolt of the gear puller that is tensioned to the shaft. Give it 3-4 healthy whacks. Retention the gear puller then give it three more whacks. You may need to repeat 10-20 times or more but you'll eventually inch it off welded or not.
From contributor J:
In all reality if it is welded to the shaft you are better off getting a cutting torch and replacing both head and spindle. That is a bit of an extreme measure though, try this first: I have seen heads which appeared to be welded/stuck on a shaft, when in fact it was because the knives were left hanging just a little out of the head on the bottom side of the head. The tips of the knives get stuck on the shaft collar. Take all the knives out of the head, gibs, and filler strip. This will release a lot of pressure, and it will also give you additional clamping points for the gear puller. Then try to pull it off.
From contributor A:
We all know penetrating lubricants. Like "Liquid Wench". But most people have never heard of a brand called AeroKroil (sometimes called Kroil). It is only available mail order direct from the company. That stuff is the real deal. It's used by aeronautic firms to get stainless fastners out of aluminum.
It's is extremely thin. We had some heads awhile back that the gib screws would seize every time we time we used them. We tried every lube known to man then someone put us onto AeroKroil.
I've used in marine situations where there was severe electrolysis between stainless and aluminum. Also steel nuts rusted onto steel bolts. It works in ten minutes in the worse situation – there is nothing like it. I suggest everyone get a bottle in advance to have on the shelf. It's also cheap. The other trick you might try is to get some C02 and freeze the spindle before heating the head.
From contributor C:
Heat, heat, heat. If you don't get it so hot you change the temper, you will not hurt it. I don't know how your spindle is made, but if you can remove the spindle and the head from the machine and there is any length to the spindle, it will not heat as rapidly as the head.
All you are doing is the reverse of a shrink fit, which is fairly common. Removing the knives and gibs is the correct thing to do, as pointed out above, because that will make the head easier to work with.
From contributor R:
Whacking it with a hammer will only make matters worse, particularly if the spindle is still in the machine. Spinning the head and thus welding it to the shaft damages both. You can pull the spindle and take it to a machine shop and maybe have it pressed off, which will further gall the shaft as bits of metal will be dragged with it. Bottom line, the spindle will probably need to be rebuilt and the shaft replaced to ensure a good finish. Take it to somebody who knows what they are doing for evaluation and repair and get back to work.
From contributor C:
We do this type of work in our shop almost every day for the local manufacturers. If you are not near High Point, there must be a similar shop in your area. I never heard of AeroKroil, but I sure do intend to give it a try.
As pointed out above, the worst thing you can do is force the head without using some other measures such as heat and dry ice combo, or you damage both the spindle and the head worse. Score marks and metal chips will build on each other and you end up with a real mess.
From contributor M:
I have also spun a head or two the worst be a hardened insert head. We applied so much pressure with the puller we destroyed the spindle. I would take a good look at the value of the head versus spindle and make your decision from there. If it is on there well, meaning heat doesn’t work you may want to pull the spindle and have it machined off on a lathe by a machinist. It is amazing how little galling it takes to get it stuck on the spindle but if you cannot drag the galling up the spindle you have a lot better chance of saving the spindle. The hardened head I mentioned was as tough as the spindle so they both were a goner, but traditional straight knife heads are typically quite a bit softer. Freezing the whole spindle assembly before heating the head can help increase the expansion difference this all assuming the spindle can be removed with the head on it like ours can.
From Dave Rankin, forum technical advisor:
We rebuild a lot of spindles and this is a common problem. When I need to remove a welded head, I do the following:
1. I remove all of the knives and gibs from the head.
2. Remove the spindle from the machine.
3. Using a press, a apply pressure, normally not over 15 tons, making sure to secure the head against the press rails. Place a board under the press to catch the spindle if it does move.
4. If this does not do the job, I try heat.
5. Lastly, I turn the head off of the shaft on a lathe.
After spinning a head, the spindle may need to be built up or replaced. Most of the time a complete new spindle is not needed.
From contributor A:
If you can get the spindle unit out of the machine throw it in a freezer for a morning. Then use a propane torch to carefully heat up the head while pushing with the gear puller.
From contributor U:
Order a new spindle, and when it comes in put the old spun shaft and spindle in the same box and let a professional analyze your situation. You will probably have to replace shaft, bearings, and you will now have a spare in case you do this again. Having the spare will keep your moulder running in times like these.
From contributor U:
I don't know if this will help you because we don't know how many spindles are on your moulder. If you have a 5 spindle machine you could take the second bottom spindle and put it in the top position. Check the length they are most likely the same. Now you could get some work done till your new spindle arrives or the old one is fixed. There will be products you won’t be able to run, but you could at least run something.
From contributor Y
It is actually less expensive to have the manufacturer rebuild the spindle because they give a warranty. To avoid this problem in the future, check the shoulder of the spindle, your spacers, and locking nuts for burrs, which mostly are caused by shavings impacted on the surfaces. Clean the surfaces, and please do not use emery cloth or something aggressive that ruins the above mentioned. It is possible that when the cutterhead was tightened the contact point was the burrs, henceforth starting up the spindle caused the cutterhead to slip, which is heat, the rest you know.
From contributor L:
Just one caution about smacking the end of the pull bolt that is pushing on the shaft. It’s not a good idea as it may cause bearing damage. It’s ok if you can get the shaft out of the machine free of the bearings.
From contributor O:
I feel I need to give a little back ground on this pulling and tapping technique. I ran a moulding mill with two Weinigs for 15 years. During that period of time I trained about 20 moulder operator as well as operating the moulders myself for over 10 years. Every operator (even the good ones) will spin a head a time or two in their career. The good operators are often very distraught about spinning a head. So including the 1 or 2 times I’ve done it makes about 30-40 spun heads I’ve had to deal with.
Tapping the back of a gear puller is a very common mechanic technique for pulling anything from rusted gears, to bandsaw wheels, to ball joints etc. And it works. There is less chance of "bending" the shaft with a short straight-on tap than with a press. Also this technique is quick. You can be back up and running in 20 minutes. Time and customer relations in this industry cost alot of money too. Of course if you get carried away with it you can damage the bearings. But with a moderate stiff whack I never had long term damage on any of my spindles.
Let look at gauling (scratching the spindle). When a head spins (welds) it creates a small ring shape weld usually only about 1/16 wide. Usually there is a prominent one on one side of the head and a less prominent one on the other side. The chips flaked off from the weld are usually 1/32" deep by 1/32" wide. Unless your heating techniques opens up the bore by 1/32 you’re still going to get gauling. However I admit that it could minimize the gauling as much as it could be. Not a bad idea, however I’m not sure about putting pressure on a hot head with a gear puller.
Also, not every spin of the head is terrible. Some are pretty minor and with a tap or two pop off with hardly any damage to the shaft. When I talk about emery cloth on the shaft, I use emery on a wood block so I can pinpoint sand on the damage of the weld or scratch and nothing else.
I never had a situation of a single spin incident leading to needing the shaft to be rebuilt. After 12 years I put a new top profiling shaft on one of our moulders. If you’re running jointed shaft damage will show up in your finish much quicker.
This technique is simply an option that works proven over years of experience. If you want to rebuild your shaft every time you spin it go ahead. If you want to send it to the "professionals" every time go ahead.
From contributor L:
I agree there is a difference between smacking and tapping. I grew up in the excavating business where the equipment was subject to the worst possible conditions, dirt, water, sand, so things could get really tough to pull. Big pullers, often hydraulic, and an 8 lb sledge to tap with! My point was it is quite possible to damage the bearings and then be down even longer.
From Dave Rankin, forum technical advisor:
Recently we have had two cutterheads spin on the shafts at different customers. The first head required minimal pressure to remove. The shaft will need to be replaced or repaired. The customer decided to have the spindle repaired with chrome. Over the last many years, building up a shaft has saved the customer money and provided a higher quality surface for the cutterhead to slide onto. For hydroheads, it provides a very secure locking area.
The second spindle has the head severely stuck in place. In this case, we will apply minimal pressure prior to using heat or cold. Note: on spindles with an outboard bearing it is very easy to bend that smaller diameter area of the shaft.
It is very common for customers to request that we reuse the bearings. When a spindle is being disassembled, the chance of saving the bearings is extremely small. It is not worth the risk for the minimal money savings. Downtime alone will offset the potential savings. If you are unsure about a welded cutterhead, send the spindle/cutterhead to a professional service. This may be the manufacturer or a qualified manufacture trained service.
