How to measure/replicate an internal taper?

[MikeInOr]

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Seems like a straight bore & pin would be a better solution. That taper is going to lock and be a PIA when you are trying to rotate the eccentric.
I had an SCM slider, 8'+ stroke & 16" blade. Straight pins! Very good saw.

The fence get removed frequently so the pin get removed frequently. The eccentric should only need to be adjusted once and the fence should line up every time the fence is put back on the table.

 

[Larry$]

Will a tapered pin want to lock into the hole and make it difficult to remove the fence?

 

[RJSakowski]

I think you want the plug to register on the extremes of the internal taper, so you want the diameters of the plug to be significantly different. Other than for aid in establishing concentricity, the absolute length of the plug shouldn't matter as it gets subtracted out.

You are correct. I should have said the difference in positions measured when the plug is reversed. From a practical standpoint, a longer plug is easier to align with the spindle axis.

 

[durableoreo]

Grease the hole and plug it, then pour in some melted metal (old car wheel
weights?). Pop the plug out when it sets. Coathanger wire inserted as a handle?

I've used plaster of paris, too, in making replicas of things that need to fit.

Chuck the taper replica in your lathe, center it, and adjust the compound until it's parallel.

This is a fine idea... for a gunsmith. Woods metal or some other bismuth alloy that shrinks very little. McMaster has a selection but they're expensive.

I think RJ's suggestion is the way to go. Any bit of scrap will do. Ball bearings are more reliable but do you have the balls you need for this particular hole?

Oh no. Now that I have all the gage pins, I'll have to obsessively collect all the sizes of ball bearings.

 

[MikeInOr]

After hours of messing around and chewing up a foot of aluminum rod I have figured out the holes are indeed straight... meaning I wasn't very careful measuring them in the first place. I am going to blame my glasses, straight lines are no longer straight.

After cutting many rods with ever more gradual tapers I finally figured out at roughly 0.5 degrees that the holes are straight. When I push the 0.5 degree taper into the holes firmly they leave a ring around the taper at 0.635" which is roughly 16.129mm. I am thinking that the original pins were probably 16mm... it is an Italian saw probably from the 1980's.

My thought is to order a 16mm rod. cut the bottom off at 45 degrees and make a 16mm diameter 45 degree wedge nut to bolt onto the bottom of the rod which will wedge into the hole when the bolt is tightened.

The whole purpose of a sliding table saw is to be able to keep tighter tolerances on cut angle than can be achieved with a miter saw or radial arm saw. (Please no discussion that such accuracy isn't needed for woodworking.) Having both ends of the fence jostling around at ~0.13mm kind of defeats the purpose of a sliding table saw no matter how insignificant that may be for woodworking.

Or should I just try to turn rods that are slip fits for the holes and stop there?

P.S. I liked the idea of filling a hole with molten lead to measure but I don't have any lead laying around. I also don't have gauge pins or gauge balls.



At 1/2 degree on the compound I finally figured out the hole was straight

 

[RJSakowski]

Making tight fitting miter joints is a challenge. Even more so when when a miter is on either end. I had occasion last year to make miters with a 20º angle and was perplexed at how to cut it. My compound miter saw won't cut tha sharp an angle and even it it would, holding a four inch piece while cutting it is virtually impossible. Likewise, I couldn't use my table saw or my radial arm saw. I ended up cutting the pieces on my mill, using the rotary table and a carbide end mill. The angles came out dead on and the finish was better than anything I could do with my wood working tools.

 

[Smithdoor]

This is the out-rigger to my sliding table saw.
View attachment 477336


The two tapered holes at the top and bottom of the picture are where the fence mounts to the sliding table. I do not have the fence or the pins that go into these holes. The bottom hole is an eccentric for adjusting the fence square to the blade.

View attachment 477344

I need to make the tapered pins that go in these holes. How do I figure out/replicate the taper I need for cutting new pins on the lathe?

The fixed hole is .609" at the top wide part of the taper.
View attachment 477346

It is .553" dia at the bottom of the hole.
View attachment 477347

The hole is 1.53" deep (the thickness of the table).
View attachment 477348


The eccentric hole appears to be a steeper taper and has a ridge about 3/4 of the way down the hole making it much harder to measure.

I am tempted to drive a soft wood dowel (or maybe a candle stick?) in the eccentric hole, mount the dowel in the lathe then set the compound slide angle to closely match the compressed wood taper.

Any suggestions would be appreciated!

I have used lead to find the tapper and some type of wax like protection on tool which the cheapest and low temp under 350°.

You can use a low temperature metal too. Epoxy also works

Dave

 

[Firstram]

holding a four inch piece while cutting it is virtually impossible. Likewise, I couldn't use my table saw

The answer is, always build a saw sled for your table saw. Sliding saw accuracy and safety, on a budget!

 

[RJSakowski]

A sled for the table saw is a definite improvement. I'm not sure that it will meet standards for thousandths level accuracy though. I did some investigation when I was looking at tightening up my cross slide and the table slot wasn't totally uniform along its length. I didn't check the two slots for parallelness which would be a requirement for proper sled use.

 

[Firstram]

A sled for the table saw is a definite improvement. I'm not sure that it will meet standards for thousandths level accuracy though. I did some investigation when I was looking at tightening up my cross slide and the table slot wasn't totally uniform along its length. I didn't check the two slots for parallelness which would be a requirement for proper sled use.

Use one slot and true the trunion to that. I can get very repeatable cuts with consistent motion on a loose sled. Thousandth's, no. Fine tooth box joints on an 8 inch part, all day long!