Crosscut Sled Sustained Accuracy

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dusty
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Re: Crosscut Sled Sustained Accuracy

Post by dusty »

JPG wrote: Fri Jan 08, 2021 9:50 am The repeatability of the 'rubber bumper' has always concerned me. I have far greater faith in the repeatability of the M5 plastic ring. I think having a ring on both way tubes would be more accurate. As mentioned, as accurate as it needs to be for what we are doing. Rigorous consisent seating of the saw arbor on the quill shaft etc. is necessary.
If I had to make a guess I would say that you have not used a setup that utilizes the rubber bumper. I say that because in my experience using the rubber bumper is very reliable and I use a NZCI almost exclusively.
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dusty
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Re: Crosscut Sled Sustained Accuracy

Post by dusty »

RFGuy wrote: Fri Jan 08, 2021 12:33 pm Unless the OP replies again on this thread to clarify, I don't know that their question was 100% clear. My interpretation of their question is with regards to the sawblade placement relative to the miter bar slots. Some Shopsmith owners rely on the rubber bump for carriage alignment and others don't. I use mine, but even so I can see 1-2mm of slop easy. It is enough that over time my ZCI insert becomes just an insert, i.e. not zero clearance any more and has to be replaced. This is despite trying to align the carriage perfectly every time so the sawblade is centered in the ZCI. So, I am assuming it is this horizontal alignment that the OP was asking about. Am I the only one having ZCI issues due to my inability to keep perfect spacing of headstock <-> carriage?

Keep in mind that crosscut sleds can be used for many functions, e.g. some set them up to do box/finger joints, etc. so maintaining a good alignment between headstock (sawblade) and carriage (miter bar slots) can be important for some repetitive cuts, etc.
I reread this and I do agree. Over time there is clear evidence that the blade does not come up (thru the ZCI) in exactly the same position every time but I believe that is as much the result of NOT sliding the carriage tight against the rubber bumper everytime.
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reible
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Re: Crosscut Sled Sustained Accuracy

Post by reible »

When I look at my crosscut sled I see where either I did not get proper alignment or used a different width of blade. (The insert in the crosscut sled on mine are replaceable.)

I don't even think about how accurate the bumper is because it isn't. I spent a far amount of time trying this and measuring the results, they were not good if you hoped for an actual zero point. I even spent some time developing a part to fit between and have some degree of control and fine adjustable control. Without actual machined surfaces to interface with even this did not get the results I wanted. I have planned to file flats on the two parts and I do believe that might work but have never gone back to attempt this project again.

So ZCI doesn't need to be an issue. The best way to deal with this is to lower the table over the blade with the blade locked in position. You can then adjust the quill to get a centered location in the insert if needed. You can hand spin the blade from the none blade side and get just about a perfect fit this way. I have also found that a small amount of extra width doesn't effect the cut much or does it cause me to want to replace the insert for most work.

If you can I would suggest that you add replaceable strips in your crosscut sled. That way this all becomes a mute point. I sometimes use a dado blade in mine, wouldn't do that unless the strips were replaceable. It just makes sense to do so. You of course can do as you see fit.

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Re: Crosscut Sled Sustained Accuracy

Post by RFGuy »

reible wrote: Fri Jan 08, 2021 2:13 pm
So ZCI doesn't need to be an issue. The best way to deal with this is to lower the table over the blade with the blade locked in position. You can then adjust the quill to get a centered location in the insert if needed. You can hand spin the blade from the none blade side and get just about a perfect fit this way. I have also found that a small amount of extra width doesn't effect the cut much or does it cause me to want to replace the insert for most work.

Ed
Thanks Ed. Yeah, this is exactly what I do every time. I slowly lower the table and try to adjust the carriage left/right to get the ZCI to slide around the sawblade. Also, I am using the same Forrest blade every time. Most of the time I am making a cut with just the main table alone, so perhaps the "play" the main table has causes the ZCI opening to grow wider and wider over time. I would have to try with a fresh ZCI and always use connector rods between the main table and aux table to see if by stiffening up the main table if I can prevent some of this "slop" that invariably creeps in to my cuts. Another alternative is I could rely on the rubber bumper alone and see how much it moves each time. When I attempted this before though I noticed that I could not always lower the sawblade into the same ZCI slot, i.e. it would hit on one side.

Thanks for the suggestions.
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Re: Crosscut Sled Sustained Accuracy

Post by bainin »

Seems like a replacement spacer for that rubber thing could minimize variance on that part. Maybe a piece of hardwood or something?

I use the rubber stop as a first approximation-but then move the table a bit back and forth to align with ZCI. Final test is hand rotating the blade to listen for rubbing against sides of ZCI.

b
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Re: Crosscut Sled Sustained Accuracy

Post by edflorence »

My '54 carriage has a "positioning stud" that works fine. The stud is a threaded bolt that screws into threads tapped in the carriage. There is a nut that tightens over the stud to lock it into place once the stud adjustment is done. This arrangement serves the same function as the rubber rings, but with no "slop" or change due to compression of the ring. It seems like it would be pretty easy to retrofit a newer carriage with this setup.
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JPG
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Re: Crosscut Sled Sustained Accuracy

Post by JPG »

garys wrote: Fri Jan 08, 2021 11:29 am If you leave it off completely, you don't have the thin one acting as a bumper between the headstock and the table. Do you want to bang things up or cushion them?
Not much different from a hard plastic ring.

The spacer separates the headstock and the carriage.
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