a mechanical engineering calculation for my new table saw

[devonwoody]

I would like to make a gadget (jig) that would enable me when setting the rip fence on my new tables to work to less than one millimeter.

The idea has been created by seeing a proprietary tool.

Can anyone tell me or direct me to where I can get the information on the measurement travelled by one revolution of a bolt head through its thread (M5/M6 or M8 ) also it distance travelled at each flat of its bolt head.

Picture below to demonstrate my thoughts:-

The bolt comming through moves a certain distance which can be utilised to push a fence inwards or outwards depending on its table location.

 

[gav]

Hi,

There was a discussion on this in this thread and theres a table for a range of metric screw sizes

https://www.ukworkshop.co.uk/forums/viewtopic.php?t=5151

Gav

 

[devonwoody]

Thanks gav, I missed that one back in May.
All the information is there.


Thinking of anchoring the block down on the table adjacent to the fence with earth magnets.

 

[Chris Knight]

Micrometer heads are usually available on Ebay for a song and are much better than bolts for this purpose http://tinyurl.com/9fzeu

 

[Argee]

You might find this pdf file gives some inspiration, albeit that it's for a different saw.

Ray.

 

[Woody Alan]

DW

Having spent all that dosh on the new saw wouldn't it be easier/time saving/neater to buy the proprietary micro adjuster from scheppach. I find it works very well. This adjuster comes as standard with the 4010 but is optional with the 2500.

Cheers Alan

P.S they're not cheap though

 

[devonwoody]

You might find this pdf file gives some inspiration, albeit that it's for a different saw.

Ray.

Thats a nice little beauty, should keep me going for a couple of afternoons making something like that.

Woodyallan,I've got to stop spending somehow

 

[Johnboy]

The problem with using a screw or bolt is that there will be quite a lot of "backlash" or free play when changing direction. A micrometre head as suggested by Chris solves this and give you a direct reading of the amount moved as well. I fitted one to my homemade tenoning jig and it works a treat.

John

 

[devonwoody]

Sound advice Johnboy, but would fine thread work satisfactorly, and what thread do scheppach use?

 

[Johnboy]

Don't know about Schepppach but my Kity 619 uses a 1mm pitch (each full turn moves the fence 1mm) screw. This is OK if you keep adjusting in the same direction but has backlash when reversing direction. You will have this problem with any ordinary screw/bolt. It is not a big issue but the micrometre head is better.

John

 

[devonwoody]

Been playing with my calliper on the saw fence this morning and I've got a backlash problem anyway when I push the clamp down on the ruler bar so will have to think some more or get advice before I start down this road.

I am having to make a compensation adjustment to the eye glass gauge to compensate for this movement that occurs.

 

[PhilipL]

Mark Duginske's DVD "Mastering Woodworking Machines" has a very elegant idea on 'micro adjustment' - that is to use pieces of paper between a fence and a false fence. so that you start with say 10 (at .004" each or about .1mm, I seem to remember) and remove these one by one until you get the required result. This would perhaps be a more accurate method when working at parts of a mm, than trying to work with a bolt.

It seemed like a very simple and effective idea to me, without the expense of micro-adjusting hardware. I pointed to this on another thread - perhaps it's a better known technique than I imagine.

Philip

 

[Woody Alan]

DW

At the risk of repeating myself, Scheppach do a very nice purpose made bit of kit for this and it has 0.1 mm adjustments marked. One full turn of the indexed knob is 1mm it's possible to set it to 1/2 of 0.1mm. If you're really trying, it could be argued that there is 0.1mm of backlash. As for backlash on the fence itself I can't see how you can avoid any play prior to clamping on the rail. Fences to that standard don't exist at this level, do they?. The measuring scale on the fence bar for my purposes is only for reference at best. There is the blade kerf/sacrificial fence/which way the fence is attached, all of which render the scale meaningless. I am used to setting mine from a tape measure,(in itself inaccurate but I use the same one through a project) locking the fence, measuring again to see how far out it is, release fence and use micro-adjuster to suit. I really can't see when you're going to need this accuracy? Johnboy has fitted one to a tenoning jig but that is to be able to cut an accurate joint.

Hope that's not coming over the wrong way, but nobody has yet said that they were troubled by it and solved it in a particular way themselves.


Cheers Alan

 

[Bean]

If its the final positioning that concerns you, or rather the actual amount you are moving then use a measuring device that removes the effect of the backlash, Buy a cheap digital vernier cut off the jaws and use the rest fixed to the crude fine adjusted (simply a m6 bolt through a block to push with, the end of the bolt could be fixed and then it will also pull. But the vernier will give you an indication of how much you have moved the fence and in which direction.

Alternativly you could buy one but that will not go to 4 decimal places and is not as much fun as making one yourself

Bean

 

[devonwoody]

The idea arose because scheppach have this item for sale as an extra to the basic model supplied.

Oddly enough there is a similar device already fitted as standard on the sliding carriage fence and I found it very nice when making an accurate crosscut for joint and obtaining timber cut to a specific length.

However I wonder about the idea of spending to obtain this accuracy when ripping because invariably I am going to put the ripped piece through the P/Thicknesser. ( Thats another story, seeing I twist the thicknessing handle by experience and get to my required dimensions, sometimes )

Will most probably cobble a device one day to set the ripping fence and post my masterpiece