Can You Get Perfect Horizontal Alignment By Squaring the Headrest?

algale · Post by **algale** » Sat Aug 18, 2012 5:59 pm

Those not interested in problems that are more hypothetical than real should stop reading now.

In another post, http://shopsmith.net/forums/showpost.ht ... ostcount=6 I suggested the horizontal alignment between an SPT with straight mounting tubes and the upper aux spindle could be achieved by loosening the bolts securing the bench tubes to the headrest and twisting/skewing the headrest. I had picked this idea up from some posts JPG and Bill Mayo had made.

It turns out there's an old Shopsmith/Magna publication called "Additional Horizontal Adjustments" that shows this adjustment (in addition to using the leveling screw under the tie bar). I found it by Google searching the forum. Here is the link: http://www.shopsmith.net/forums/attachm ... 1275673577

In my earlier post I mentioned that I was going to experiment with this idea this weekend. I have. The results are not what I expected.

First, to test horizontal alignment, I decided I needed something without eccentric tubes. So, I mounted the lathe tailstock in the headrest (left side) and put my live center in the lathe tailstock. I then mounted the drill chuck on the upper aux spindle. Then I moved the headstock to the left until the drill chuck nearly touched the point of the live center. (This is the same method Shopsmith outlines for alignment the lathe tailstock on the right side; just moved to the left side.) Here's a picture of the test setup. [ATTACH]18215[/ATTACH]
Seen from the side, it looks good. Seen from above, however, the horizontal misalignment becomes clear.[ATTACH]18216[/ATTACH]
There's a little parallax in the photo, but trust me, if I bring the headstock over, the point of the live center just barely misses the closed tip of the drill chuck, so the misalignment is slightly greater than the radius of the closed tip of the drill chuck, perhaps 1/8 of an inch.

Taking my own advice, I loosened the bolts securing the bench tubes and attempted to turn the headrest to bring the point of live center into the center of the drill chuck. Despite my best efforts, I cannot get anywhere near horizontal alignment by "squaring the headrest." Not surprisingly, there's a limit to how much you can twist the headrest on the bench tubes and it just isn't enough.

This isn't a practical problem since I have eccentric mounting tubes on my bandsaw and beltsander that allow perfect horizontal alignment. I could also use the leveling screw under the headrest to achieve perfect horizontal alignment, but since I have already taken the twist out of the way tubes using the leveling screws, would I be introducing a different error (twist) by doing so?

Incidentally, I am curious if people have opinions on the cause of this misalignment. It occurs to me that the belt tensioning/eccentric bushing could cause the aux shaft to have a different axis of rotation than the main spindle but as I sight down the headstock, the aux spindle seems to be in line with the casting ridge on top of the headstock and with the main spindle. In contrast, the lathe center clearly is not in line with the casting ridge or the main spindle. So, what causes this?

Anyone with a double tile upgrade care to experiment and see if they do or do not have this same misalignment issue?

Al

holsgo · Post by **holsgo** » Sat Aug 18, 2012 9:09 pm

I should have stopped reading since I can't understand why you would care about this mis alignment.

algale · Post by **algale** » Sat Aug 18, 2012 9:39 pm

holsgo wrote:I should have stopped reading since I can't understand why you would care about this mis alignment.

Well, you were warned at the beginning.

To answer your question, however, I care about this misalignment for several reasons. First, I believe it is the reason that an extension table aligned perfectly on the right side won't align horizontally on the left and vice versa. If the root cause of this type of misalignment were understood, perhaps a solution could be implemented.

Second, that same solution would presumably be useful for people using SPT's on straight (not eccentric) legs. I know that the standard solution is to use the leveling screw to compensate for the horizontal misalignment. I suspect that this solution creates a different problem: by putting additional twist on the way tubes it would seem likely to make the main table and extension tables not coplanar (another reason why extension table alignment may be lost moving from right to left or vice versa).

Third, I'm generally fascinated by this thing called the Shopsmith and I like to understand why things on it work or don't.

holsgo · Post by **holsgo** » Sat Aug 18, 2012 9:51 pm

Ok. Just not my type of issue I guess.

jimthej · Post by **jimthej** » Mon Aug 20, 2012 1:16 am

Are your tubes fully seated in their sockets? On both ends? Would some adjustments there improve your alignment?

charlese · Post by **charlese** » Mon Aug 20, 2012 1:28 am

Seems to me, Al, that when you moved the tail to the other side of the machine, any offset you had on the true tail would be reversed on the other end. Offset to the right becomes offset to the left.

"Kinda like" the counter clockwise rotation of the quill becomes clockwise rotation on the auxillary spindle. (not really a good comparison but reverse remains reverse)

michaeltoc · Post by **michaeltoc** » Mon Aug 20, 2012 6:26 am

algale wrote:Despite my best efforts, I cannot get anywhere near horizontal alignment by "squaring the headrest."
Al

My guess is that both ends must be perfectly perpendicular to the tubes. Everything is aligned to the right side, but if that end is not perpendicular to the tubes, then you can never get the left side aligned to the right. It would seem that you need to loosen both ends then square them both up to the tubes.

BTW - your offset of 1/8" may seem like a lot, but 1/8" over 6' is only 1/10th of a degree.

algale · Post by **algale** » Mon Aug 20, 2012 8:26 am

charlese wrote:Seems to me, Al, that when you moved the tail to the other side of the machine, any offset you had on the true tail would be reversed on the other end. Offset to the right becomes offset to the left.

"Kinda like" the counter clockwise rotation of the quill becomes clockwise rotation on the auxillary spindle. (not really a good comparison but reverse remains reverse)

That would be true but if you are referring to the tail stock eccentric, it was already set to "zero."

algale · Post by **algale** » Mon Aug 20, 2012 8:33 am

jimthej wrote:Are your tubes fully seated in their sockets? On both ends? Would some adjustments there improve your alignment?

The bench tubes are fully seated up against the stop ribs in the base arm (right end); but the headrest (left end) has no stop ribs, so I am not sure what would qualify as "fully seated" on the left.

Meanwhile, my misalignment problem, has been greatly improved. I took the machine apart again and built it back up again. This time I squared the headrest by using a piece of wood as a spacer between the tie bar and the headrest in an attempt to set a consistent distance. The result was much closer alignment. I will post pictures this evening.

Al

dusty · Post by **dusty** » Mon Aug 20, 2012 9:11 am

I am curious. Can you tell me what the distance is between your bench tubes. I measure mine at 6 3/4".

If this distance is consistent the full length of the bench tubes, the tubes are parallel (assuming they are in the same plane). Then, if seated against the stop ribs in the base arm, I don't see how you can go wrong (alignment wise).

On my unmodified Mark V, the exposed bench tubes measure exactly 4'. That distance is somewhat dictated by the length of your way tubes. If the way tubes are properly seated on both ends, the end to end length of the Mark V is dictated by the length of the way tubes. The location of the headrest must be adjusted on the bench tubes to accommodate the length of the way tube assembly.

I hope this information is consistent with your findings and does not cause any confusion. I wish you well on this endeavor. I still suspect that the only way to achieve life long consistency is to upgrade to a double tilt. Even when perfectly assembled, the only thing holding every thing in alignment is the pressure applied by a few set screws against the tubes.

PS: Your way tubes are both the same length, right. The two bench tubes should also be equal in length and 3/4" longer than the way tubes.