Thread: Blade alignment changing with height?

I did some checking and it turns out the two shafts are co-planer and the pivot shaft is perpendicular to the machined face (right side pictured), but the arbor shaft is about 2 degrees away from perpendicular to the machined face. The picture shows the way the arbor shaft is currently out of alignment.

All the other factors in this problem turned out ok, so the good news is there is only one dimension that needs to be addressed. The question now, is how? About the only thing I can think of is to cut the whole thing in half and bolt a couple of steel plates on the top and bottom of the hollow to get the alignment right, then weld it back together. I'm confident arc welding steel, but cast iron I've never done before, is this a really bad idea?

I'm open to suggestions... please!

Dave.

Something has changed. I presume it used to cut ok. Check the arbor bearings and bearing housings.

I only recently purchased it second hand. It cuts very well as long as the height isn't changed, which is quite dangerous of course.

The bearings are fine, no play at all, just a tiny bit rough. The tolerances are all great, it looks like it machined incorrectly in the first place.

I would get the arbour out and as a matter of course replace the bearings, but also check that the arbour is straight, it may have a bend in it depending on how it was pressed in the last time.

I've checked the arbour run-out and shaft straighness, both are within 0.001" checked with a dial gauge. To give you a little perspective, the centre to centre distance between the pivot and the arbor shaft measured at both sides of the arm differ by 0.022", or 0.58mm. My original estimate of the degree of misalignment based on the measurements taken from the blade alignment was 0.6mm.

A problem with the system of this magnitude would be easily visible; massive play in the shaft, gross wear of bearing surfaces, etc. In this case all of the tolerances are very good, even the bearing surfaces of the pivot pin are <0.001" out-of-round (my equipment can't give me a reading more accurate than this) with 0.003" of clearance and no measurable wear. Nothing points to any problem other that a manufacturing fault.

The quest really is, how do I fix it?

I reckon I'll post in the metalwork forum too.

Can you bore it out then sleeve it?

It's possible but could become very expensive. Cost is a big factor for me, so a cheap solution is far better. I might hunt through the yellow pages and enquire at least.

Douglas ,

Cast iron welding is difficult ,the problem is the heat range that is needed to weld it successfully its either done stone cold or red hot , nothing in between .
No Guarantee that it will be parallel when you are finished either.
You may still have to have it bored out after welding.

Does the arbour shaft run in bronze bush type bearings in the casting or does it have ball /roller bearings?
I would have it bored out over sized and parallel to the pivot shaft then sleeved with heavier bronze bushes with a bore to suit the arbour.

If it has roller or ball bearings I would still bore it out and sleeve the bore , probably scotch key the bore inserts into the casting and then bore the inserts out to fit new bearings.

It is a fairly simple job , for an experienced machinist , could be done in large lathe or on a milling machine .or a jig borer .

Originally Posted by kman-oz

I only recently purchased it second hand. It cuts very well as long as the height isn't changed, which is quite dangerous of course.

The bearings are fine, no play at all, just a tiny bit rough. The tolerances are all great, it looks like it machined incorrectly in the first place.

I would contact the Seller and explain the situation, returning the saw if you could. While the Seller may not have known about this fault, if the saw was used a reasonable amount it would be a hard to miss.

You could also try the manufacturer/agent first and see if they will honour a warrantee owing the evidence of a factory fault.

This repair may be uneconomical.

Regards from Perth

Derek

Derek, I purchase second hand in the full knowledge that this sort of thing will happen. As a matter of course I'd check an item over to make sure all is well at a glance, but I will philosophically accept that there will be stuff that needs to be addressed. I don't object to people working that way, but I don't work that way.

I'll try the warranty option, you never know.

Woodlee, thanks for the advice on welding, it seems everyone dislikes this option for the same reasons. I'm beginning to agree that the only reasonable way to do this repair is by milling the bearing seat out and bushing it as you suggest.

It's a sealed ball bearing system (17mm ID, 40mm OD, 15mm W) pressed into the arbor arm. For a while it looked like a special bore size to suite the arbor shaft, but I was able to measure the bore at 17mm which is a standard size.

I wonder of boring the bearing seat to 47mm in the correct position and using a 47mm OD bearing would be a suitable solution? Or do I risk thinning the walls to much? I might take a couple of photos of that to giv you an idea.

Dave.

It would depend on the out side dimension of the casting how far you could go . If you bore it out and sleeve it and go back to the original od of the bearing there should not be a problem .
I would definitely scotch key any sleeve into the casting ,so you would need a bit of meat to take the scotch keys.
Say 5mm thickness each side of the bearing od

Kev.

How much to just replace the parts? Assuming you can't get any satisfaction from the manufacturer. That also assumes that the manufacturer will cooperate in getting said parts. My experience with a certain manufacturer's local agent (beginning with the letter J...) in trying to buy a low profile riving knife for my new saw suggests that may not be simple either. I ended up ordering the part from the US.

I'd taken the arbor lift arm to a couple of engineering mobs and they told me the same thing; 'It ain't worth fixin'. Easy for them to say! The other outcome of this was some more accurate measurements of the critical geometry, which turned up a few more faults. By the end of this time it was quite obvious that the manufacturing quality just wasn't up to scratch and that a replacement part would be no better.

So, one pillow mount bearing assembly, some steel angle, an 8mm tap and tap wrench, a few nuts and bolts and it's all fixed. Those years spent in a tech school paid off

I whacked it back together and jammed it into the table to see if I'd made an improvement, and the error is reduced by half without having adjusted it yet. I'll get it all adjusted up and take some shots soon.

Thanks for all you help folks.

Dave.

Here's a shot of the newly assembled component. Once it's been adjusted correctly I'll tack all the steel components in place and lock-tite the bolts.