# a boring fixture for the taig



## peatoluser (Dec 30, 2010)

i got the idea for this from Tubal Cains book 'simple workshop devices' but adapted it fit the taig face plate. I made it primarily to bore out the main bearing blocks for a triple expansion engine i'm building in another thread, but thought it may have a more 'universal appeal' so i'll post it here. I didn't take many photos when I built it but it's reasonably straight forward. 
here are the parts.





the 'angle plate' bit was made from BMS angle, but be warned, it's not 90 degrees and will need maching / filing otherwise you won't be able to bore out anything at right angles to it's base, which rather defeats the object of the fixture. As the 'lip' of the angle plate is only 5/8 wide i was happy to file this square. it's 3 inches long, so difficult to mill flat just using the lathe.
 the important point to note is the 1/4 tenon which locates in the slot in the taig faceplate. this needs to be square to the 5/8 lip to help in setting up.
apart from drilling and tapping the faceplate to accept the fixture, the other thing i did was scribe a line across the faceplate dead on centre hieght and at 90 degrees to the slot. I used a piece of 1/4 flat bar and a square to set the slot vertical. if you just lightly mark the faceplate with your scribing block, you can reset the faceplate 180 degrees to check your are scribing the exact centreline. 





the twoside arms are merely scrap pieces of 3/8 and 1/4 plate pinned together and the top clamp a piece of 1/2 by 1/4
in use ,first set the position of the angle using a ruler. just measure from the centre line, not forgetting to add on the thickness of any packing you are using. ( the bearing blocks i made had flanges and it's the height from the 'rebate' thats important not from the bottom of the flange)




to set the two arms, i turn up a setting plug, the o.d. being equal to the width of the bearing block, then just slide the arms up to it and clamp them.




you'll notice one of the arms is marked. this becomes the fixed arm and in use it's not moved. you change blocks by loosenig the other arm. if you discreetly mark the face of each bearing block as you put them in, then when you,ve bored out all the bearing blocks, the holes should all be in the same relative position as regards the base and one side.

I used this method of setting up as opposed to centre popping and using a wobble bar (?), as i find when you clamp two pieces together and try to centre pop on the joined edges , it's very easy for the centre punch to drift off.
hopefuly i've not been teaching my granny to suck eggs
yours 
peter


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