Are Your Extension Tubes Straight

[dusty]

This is an area where there has been very little, if any, discussion here on the forum. I have never even given it more than a casual thought until this past week.

One of our members has had some difficulties with table alignment and it appears that bent extension tubes might contribute to that problem.

If you needed to know whether or not your extension tubes were bent, how would you check?

If you found that they were bent, how much of a bend can your system tolerate?

[JPG]

There be different kinds of 'bent'.

The usual understanding is that they are curved someway. That may be a constant curve over the entire length, or a localized bend. Neither are desirable, but the latter can be more troublesome.

Now my tubes are bent differently.(I have not checked for either of the above, but assume they have that as well) My 'bends' are the result of PO's excessive tightening of the tube clamps. They might be more accurately described as dings or depressions of the outer(and inner when severe) tube wall. They are no doubt the result of the early clamp design which consisted of a smaller knurled 'knob' surface on the clamps AND holes through which a SS tool kit could be inserted and really torque them suckers 'tight'.

That scenario no doubt contributed to both the 510 design change and the 520 as well.

Although I have not used the 510 much since it is a project still on the to do list, I can see where the tube's lack of straightness would be more of a problem with both 510 versions than the 520. IIUC, the 520 rail is somewhat effective in forcing the tubes straight by the use of the dual tapered top surface and the directly opposed thumb screws. That does not however force them 'straight' between the floating tables, but the extension table mounted would tend to at least bring that end back towards proper alignment.

I see the tubes purpose as a support role, rather than an alignment role. That said, non-straight tubes provide a potentially cocked reference for the fence if it is being used on a floating table.

Sorry if I have gone off on a tangent here, but once started it just overflowed.

P.S. rolling them over a known flat surface would be my method of choice for determining 'straightness'. A more adventuresome method would be chucking it up and rotating the chuck and observing 'wobble'.(under power not advised)

[dusty]

There be different kinds of 'bent'.

The usual understanding is that they are curved someway. That may be a constant curve over the entire length, or a localized bend. Neither are desirable, but the latter can be more troublesome.

Now my tubes are bent differently.(I have not checked for either of the above, but assume they have that as well) My 'bends' are the result of PO's excessive tightening of the tube clamps. They might be more accurately described as dings or depressions of the outer(and inner when severe) tube wall. They are no doubt the result of the early clamp design which consisted of a smaller knurled 'knob' surface on the clamps AND holes through which a SS tool kit could be inserted and really torque them suckers 'tight'.

That scenario no doubt contributed to both the 510 design change and the 520 as well.

Although I have not used the 510 much since it is a project still on the to do list, I can see where the tube's lack of straightness would be more of a problem with both 510 versions than the 520. IIUC, the 520 rail is somewhat effective in forcing the tubes straight by the use of the dual tapered top surface and the directly opposed thumb screws. That does not however force them 'straight' between the floating tables, but the extension table mounted would tend to at least bring that end back towards proper alignment.

I see the tubes purpose as a support role, rather than an alignment role. That said, non-straight tubes provide a potentially cocked reference for the fence if it is being used on a floating table.

Sorry if I have gone off on a tangent here, but once started it just overflowed.]under power not advised[/B])

Yes, there are certainly different ways for the tubes to be bent. Some will even render them useless but I am thinking more of a casual bend like what might occur if one walks into a tube that was inadvertently left extended but secured in the extension table. Some people actually do dumb things like that.

Another way would be to leave a router table and router hanging on extension tubes with no outboard support for three or four days.

Rolling them on a flat surface certainly tells you something is not right. My wife came out to the shop and saw me doing that. "What are you doing", she asks. "Checking the tubes to se if they are straight", I respond. "How do you know the table is flat", she says as she closes the door and disappears. "I built the bench top", I thought to myself. "Certainly it is flat"!

Yes, the extension tubes are truly NOT alignment tools or guides but if they are bent they certainly do screw up what could otherwise be a perfect alignment.

With a long tube mounted in the rails and just barely secured in place, have someone rotate the tube while you watch the end of the tube in the end of a rail. If it does not wobble, you've got a straight tube.

If it wobbles, you got a bent tube that you might be able to straighten if you can tell where the bend is located and in what direction.

I have eight tubes that all wobble to some degree. I have one perfectly straight tube BUT it is only about 19" long.

[JPG]

Actually 'flat surface' need not actually be flat. Anything that provides a stable surface for the tube to rotate(a point near each end) will suffice. You can then observe any variation between those points as the tube is rotated.

Don't ya love it when the throw a verbal bomb and run?

Goes with I am right and nothing you will say can change that!:D

And they call that 'cock' sure 'thinking'.


I do not think I was around when you and Nick had that discussion, but think I agree with him that slight non-linearity of the tubes not critical. Question is, when is it greater than slight. Any curve that does not exceed the elastic limit when clamped in place is probably 'less' than too much.

[Ed in Tampa]

In the light of "If it isn't broken don't fix it" I don't know and I ain't going to check.

Actually I do know, they are for the most part straight. I have never bent (dinged) one by over tightening. I really can't imagine not knowing your putting too much pressure on locking knob to dent a tube.

My five foot tubes I keep in the shipping tube they came in so they don't get banged around or bent. When my tubes aren't in use they are stored save and secure in the table and tube holder I built and have mounted to the wall.

There is a way to bent the tubes by doing something wrong in setting up the Shopsmith I don't recall what it is but I remember seeing it done and thought to myself man that is an easy mistake to make that could be costly (buying new tubes).

[dusty]

In the light of "If it isn't broken don't fix it" I don't know and I ain't going to check.

Actually I do know, they are for the most part straight. I have never bent (dinged) one by over tightening. I really can't imagine not knowing your putting too much pressure on locking knob to dent a tube.

My five foot tubes I keep in the shipping tube they came in so they don't get banged around or bent. When my tubes aren't in use they are stored save and secure in the table and tube holder I built and have mounted to the wall.

There is a way to bent the tubes by doing something wrong in setting up the Shopsmith I don't recall what it is but I remember seeing it done and thought to myself man that is an easy mistake to make that could be costly (buying new tubes).

Ed, No argument intended here, just a couple strong opinions!

I really doubt that your tubes are all straight, especially the 5' tubes. But, if you don't look they are as straight as they ever need to be.

Furthermore, unless you use a wrench to tighten the knobs, I doubt if you can tighten them enough to bend the tubes.

[dusty]

I do believe that when it is not broke you should not attempt to fix it.

However, when I have an alignment problem that I cannot correct, I have to investigate all possible causes. While doing just that, I discovered that I do have an alignment problem that apparently had been covered up by some past corrective action that I took.

Now I am attempting to confirm whether or not an assortment of bent extension tubes that I have are contributing to this alignment issue.

By using the method shown in the following five images, I have concluded that I have NO STRAIGHT TUBES.

[ATTACH]17868[/ATTACH]
Overview of Test Method Using My Best Tube

[ATTACH]17869[/ATTACH]
Zero Left Side

[ATTACH]17870[/ATTACH]
Zero Right Side (notice the feeler gauge)

[ATTACH]17871[/ATTACH]
Rotae and Test

[ATTACH]17872[/ATTACH]
Rotate Some More and Test

[bffulgham]

I keep thinking that I need to slow down and stop by my favorite metal supply and pick up a 'stick' of 1" OD tubing to cut my own extension tubes. They won't be plated, pretty, shiny, but would sure give the ability to set up custom lengths. I'll bet they will not be perfectly straight, but my metal supply guy likes me and will let me pick and choose what 20' stick I want. They will need a good wash off with mineral spirits, or something, and a JPW and buff job for protection.

Anyone else ever tried this?

[JPG]

I keep thinking that I need to slow down and stop by my favorite metal supply and pick up a 'stick' of 1" OD tubing to cut my own extension tubes. They won't be plated, pretty, shiny, but would sure give the ability to set up custom lengths. I'll bet they will not be perfectly straight, but my metal supply guy likes me and will let me pick and choose what 20' stick I want. They will need a good wash off with mineral spirits, or something, and a JPW and buff job for protection.

Anyone else ever tried this?

Almost. Bought some 4' steel tubing when a local hardware store had a fire sale. Polished them(like way/bench tubes) and waxed them. There was little to no wobble as I spun them to polish them on the goldie. They are not as thick as OEM and I have not actually used them as intended)yet).

FWIW I discussed purchasing a few lengths(24'?) from a local supplier and he mentioned that the mfr only guaranteed straightness for 17 of those feet. Add shipping stresses to that and you may get less 'straightness'.

Dusty <1/10" over 1'('middle' to 'end') may be out of round rather than bent or both. Really not what I would consider 'a problem'.

[dusty]

Almost. Bought some 4' steel tubing when a local hardware store had a fire sale. Polished them(like way/bench tubes) and waxed them. There was little to no wobble as I spun them to polish them on the goldie. They are not as thick as OEM and I have not actually used them as intended)yet).

FWIW I discussed purchasing a few lengths(24'?) from a local supplier and he mentioned that the mfr only guaranteed straightness for 17 of those feet. Add shipping stresses to that and you may get less 'straightness'.

Dusty <1/10" over 1'('middle' to 'end') may be out of round rather than bent or both. Really not what I would consider 'a problem'.

Out of round would most probably not be a problem at all.

I won't know, until I have a couple straight extension tubes, if bent tubes even cause the issue I am dealing with.