520 carriage not sliding

[algale]

If the problem was with one of the 520 carriage bores being undersized (4 bores per carriage, 2 new 520 carriages = 8 bores!), I would expect the carriages would not to mount at all or slide at all. This has to be a tube problem.

[JPG]

Taking the details in the last post I would conclude the binding tube is the problem.

However that does not explain why only one set of carriage bores bind other than to conclude the non-binding bores are 'compatible' with the binding tube.

So back to the binding tube and binding bore.

As you suggested mark where the carriage binds on the tube from one end. Mark both ends of the carriage on the tube.

Repeat sliding the carriage from the other end of the tube.

Hopefully the two pairs of marks will be close.

Measure the locations of the 4 marks(and condition that defined them).

Clean off the marks and repeat, but reverse the carriage end for end.

Again measure the locations of the marks etc..

You should have 8 measurements.

1 distance bind occurs with carriage slid from end A.

2 distance bind occurs with carriage slid from end B.

Actually there are a pair each(both sides of the carriage). That makes 4 measurements.

3 distance from end A the carriage binds with the carriage flipped end for end.

4 ditto from end B. Again each is a pair of measurements. You now have 8.


The area between the marks are our suspicious locations. The area between the inner set of marks may be the most suspicious.

Out of round and bowed are the likely culprits. Bent also, but that should already be obvious when laid on a flat surface.

Any of this lead to new information?

[BigJohn]

Man, its all new to me. I'll make the measurements, but that begs the question, what then? I suppose the next step will be to try the new tube when it arrives and if everything slides, happy day. If that binds, I'll probably ship the tubes and carriage off to shopsmith and ask them to find a solution.

I'm going to go flip the binding tube, end for end in the holder and see if the carriage will slide from that way. Looks like i"ll have something to do while waiting for the Superbowl. I've been elected to make chilli.

Thanks again for your thoughts, I really appreciate it. Do you think the weight of the headstock could have deformed the tube over the years it sat idle(10). When they rebuilt the headstock, they said all the lubricant had run out of the bearings due to gravity over the years and the belts had flat spots.

[JPG]

Man, its all new to me. I'll make the measurements, but that begs the question, what then? I suppose the next step will be to try the new tube when it arrives and if everything slides, happy day. If that binds, I'll probably ship the tubes and carriage off to shopsmith and ask them to find a solution.

I'm going to go flip the binding tube, end for end in the holder and see if the carriage will slide from that way. Looks like i"ll have something to do while waiting for the Superbowl. I've been elected to make chilli.

Thanks again for your thoughts, I really appreciate it. Do you think the weight of the headstock could have deformed the tube over the years it sat idle(10). When they rebuilt the headstock, they said all the lubricant had run out of the bearings due to gravity over the years and the belts had flat spots.

At this point, I would look for a ding on the tube. A high spot that binds in the new carriage. Since the other bore in the carriage passes the 'ding' it will be very small. Again I would closely look at the area between the inner marks I suggested earlier.

I do not think dead weight of the headstock will have created this. Unused bearings simply dry out. Rubber belts will have flat spots over time when under tension and are never moved. i.e. no surprises re a 10 yr idle period.

[BigJohn]

will do. I'll keep you posted . Thanks again for your patience.

[BuckeyeDennis]

BigJohn, what you are observing can be explained by feature tolerances. Mechanical features are almost never exactly the “nominal” size — allowances have to be made for manufacturing variances. But if properly designed and manufactured, an assembly will still function as it should.

Here’s a scenario that would explain what you are observing.
1. The two newly-manufactured carriages are consistent with one another, but both have one bore that is slightly smaller than the other. This would be very understandable if they were both bored during the same production run, on a machine that bores both holes simultaneously.
2. One of your tubes has a defect or damage that extends very slightly outside of a circle having the same diameter as the smaller bore.
3. Both bores on your old carriage are larger than the smaller bore on the new carriage.

What we don’t know for sure is whether the smaller bores are out of tolerance on the new carriage, or your binding tube has a defect that is out of tolerance in the large direction. But if Shopsmith checked your replacement carriage, my money is on the tube being out of tolerance.

I agree with JPG’s earlier post — you can “ink” the tube and then find the binding spot by seeing where the ink gets rubbed off. That’s standard practice for machinists. They use a special “layout fluid” (e.g. Dykem”), but ordinary magic marker should work ok for this.

[BigJohn]

that's helpful! I'll make the measurements tomorrow and examine the tube closely. Thanks so much for the advice.

[BigJohn]

Further carriage antics. I am facing the shopsmith with the tie bar lock down lever on my left and the carriage handle facing me. When I slide the carriage down the tube from the left. it jams at 22 1/2 inches. If I engage only the further tube in the carriage, it slides smoothly down the whole length of the tube. If I try the other hole in the carriage and go down the further tube, it again slides smoothly down the entire length. So the hole that is furthest from the carriage wheel slides smoothly down both tubes.

If I now take the hole nearest the wheel and put the further tube in it, it jams 22 1/2 inches down the tube. It does the same thing (22 3/4) down the near tube.

If I try the same thing with the other new replacement 520 carriage from Shopsmith, I get identical results. I'm very new to this, but to my mind this would seem to suggest a problem in the bore holes in the carriage.

I took a digital caliper to measure the tubes to see if I could ge a rough estimate of roundness of the tubes. The further tube is pretty uniform along it length and about 1.74 inches in diameter as you move around the tube. The near tube begins at 1.74 but at the jam it varies from 1.73 to 1.77 so it is a bit out of round.

I tried removing the innermost tube and feeding it into the carriage from the opposite end. to my mind, this was the same as if the carriage had magically slid all the way down and was now making it way back to the left end of the machine. It jammed about 13 inches along it travel in the hole closest to the wheel. The tube may be bent or out of round along a significant part of it length?

Since it won't move close to the other jam point, I cant do a meaningful comparison of the Jam points. I checked the diameter of the holes with the calipers and they both read 1.74 inches.

I'm basically marking time until the new tube arrives, but I suspect it will also jam in the carriage.

Rotating the tubes makes no difference in the jam nor does removing the tie bar and the wedge locking assembly.

As I said, I'm very new to this having inherited the machine, and may be doing something boneheaded that is causing this. I really appreciate your thoughts and suggestions.

[JPG]

Further carriage antics. I am facing the shopsmith with the tie bar lock down lever on my left and the carriage handle facing me. When I slide the carriage down the tube from the left. it jams at 22 1/2 inches. If I engage only the further tube in the carriage, it slides smoothly down the whole length of the tube. If I try the other hole in the carriage and go down the further tube, it again slides smoothly down the entire length. So the hole that is furthest from the carriage wheel slides smoothly down both tubes.

If I now take the hole nearest the wheel and put the further tube in it, it jams 22 1/2 inches down the tube. It does the same thing (22 3/4) down the near tube.

If I try the same thing with the other new replacement 520 carriage from Shopsmith, I get identical results. I'm very new to this, but to my mind this would seem to suggest a problem in the bore holes in the carriage.

I took a digital caliper to measure the tubes to see if I could ge a rough estimate of roundness of the tubes. The further tube is pretty uniform along it length and about 1.74 inches in diameter as you move around the tube. The near tube begins at 1.74 but at the jam it varies from 1.73 to 1.77 so it is a bit out of round.

I tried removing the innermost tube and feeding it into the carriage from the opposite end. to my mind, this was the same as if the carriage had magically slid all the way down and was now making it way back to the left end of the machine. It jammed about 13 inches along it travel in the hole closest to the wheel. The tube may be bent or out of round along a significant part of it length?

Since it won't move close to the other jam point, I cant do a meaningful comparison of the Jam points. I checked the diameter of the holes with the calipers and they both read 1.74 inches.

I'm basically marking time until the new tube arrives, but I suspect it will also jam in the carriage.

Rotating the tubes makes no difference in the jam nor does removing the tie bar and the wedge locking assembly.

As I said, I'm very new to this having inherited the machine, and may be doing something boneheaded that is causing this. I really appreciate your thoughts and suggestions.

1.77 says it all!

[dusty]

What you doing is not boneheaded at all. It is a puzzle though and one thing you said keeps me wondering. I believe that you have proclaimed that the old carriage slides smoothly the entire length of the tubes. If that is correct.....how can the tube be the cause.

I think also that you said the tubes roll smoothly on a flat surface. (something that an out-of-round or bent tube would not do.

I sure do wish they would deliver that new tube. Hope you don't regret not buying two.