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Thread: Struggling with spiraling holes using PVC Jig & Forstner bit

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    Default Struggling with spiraling holes using PVC Jig & Forstner bit

    After reading a bunch on here and watching videos I made a jig using the Habor Freight centering Jig and a 1/2" doll rod. I am at a loss for why my holes are not consistent?

    IMG_9535.gif

    Here if you look from right to left each hole is slightly out of alignment with the one next to it:

    IMG_9536.gif

    How can I fix this?
    Last edited by jbourne; 09-01-2018 at 04:45 PM.

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    I have a Harbor Freight jig also and had the same problem. I had the best luck using a standard drill bit It still was not great but better. I think next time I will try a drill countersink.

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    I mounted my jig a a 1x6 board with a 1/2" dowel drilled and glued into the 1x6, dowel was about a 1/4" past the V jig and the same height.

    distance from dowel center to drill bit center adjusted to desired spacing


    Drill first hole carefully, then place it over the dowel which aligns the pvc for the next hole, drill, lift off, place freshly cut hole on the dowel, repeat until your sanity has left the building

    slightly rounding the alignment dowel end makes things easier
    Cheers!
    Steve

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    I would check that the table is perpendicular to the bit in all directions - especially the front and back of the table. I would also check whether the dowel has any play when you put a hole over it.

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    Quote Originally Posted by Aurbo99 View Post
    I mounted my jig a a 1x6 board with a 1/2" dowel drilled and glued into the 1x6, dowel was about a 1/4" past the V jig and the same height.

    distance from dowel center to drill bit center adjusted to desired spacing
    \
    That is almost exactly what I did if you look at the first photo above. The dowl is in a piece of plywood that is clamped to the drill press base with those red adjustment screws. The dowel is just about 1/4" away from the jig. I'd drill a top hole, then roll it over. But I realized something after I posted.

    The first time I attempted this the jig was further away (so the drill point was unsupported). I drilled 4-5 holes that way going completely through the bottom of the pipe with one downward pass. I quickly realized that wasn't a good way to do it and re-arranged the jig to be what you described. I think my fatal mistake is I used one of those "bad" holes as the starting point of my re-aligned jig idea, and then from that point forward all of them were all over the place.

    I got fed up with making no progress today so I went back down and built a J-Channel Jig because I'm thinking of using J-Channel along the soffits and the 1/2" PVC around the windows and the vertical corners of the house. I have to say cutting that J channel is 10x more consistent:

    IMG_9538.gif

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    The issue isn't the harbor freight piece, it is your wooden dowel. I'll try to explain. I had the same issue with my own jig, the further I went down the line the holes would spiral around the pipe.

    The wooden dowel should go through both sides of the pipe but more importantly, the wooden dowel has to be perfectly plumb (parallel) with the spindle of your drill press. The dowel has to be at 90 degrees to your work table and the spindle also has to be 90 degrees. Depending on the quality/brand of your drill press it may not be perfectly true 90 degrees. Them being off a little keeps getting magnified as you drill each hole. Also how much play is between the dowel and the drilled hole? It has to be tight.

    I ended up making one out of steel with a plate on top and bottom and using a steel pin that was removable from the top. You may not have the means to build that out of steel.

    Here is something I did before I scrapped using PVC all together. When you move the pvc to drill the next hole and place it on the dowel, place it on the dowel and rotate it clockwise for one hole then the next hole counter clockwise. This is moving the hole tight to one side then the other as there is play in your dowel to pvc fit. This will "alternate" them back and for a little bit, that won't be noticeable and keep it from spiraling around the pipe.

    I used a regular drill bit but you have to file/grind the edge of the flute so it is not too sharp otherwise when it goes through the pvc it will grab the pvc and it will shatter. Happened to me and grinding the bit fixed that issue.

    Hope this makes sense.
    J

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    remember that the alignment dowel MUST be tall enough to go through both holes you drill in the pvc pipe to maintain the vertical alignment or you will still get a spiral twist when drilling subsequent holes
    Cheers!
    Steve

    Learn 1 new thing everyday.

    "AURBO" -- Aurora Borealis

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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    Quote Originally Posted by JCook View Post
    The wooden dowel should go through both sides of the pipe but more importantly, the wooden dowel has to be perfectly plumb (parallel) with the spindle of your drill press.
    This is something I never even considered but makes perfect sense.

    The dowel has to be at 90 degrees to your work table and the spindle also has to be 90 degrees. Depending on the quality/brand of your drill press it may not be perfectly true 90 degrees. Them being off a little keeps getting magnified as you drill each hole. Also how much play is between the dowel and the drilled hole? It has to be tight.
    I am using a Crafstman drill press I bought a number of years ago, but the baseplate is a clamp on the main body post of the press. Its near impossible to adjust the height with any granularity, and it keeps wanting to spin on the post itself. I never considered that it could be causing the entire baseplate to take the dowel out of plumb let alone the fact that those two need to be perfect.

    The dowel is quite tight. Once i used a jigsaw to cut the base plywood to be the shape of the drill press I marked the oval holes in the drill press baseplate and also notched those out with the jigsaw (so I could attach the plywood to the drill press baseplate firmly). Once that was done I bored a hole right through the plywood and considered that my dead center. I measured off to the right 2" on center and drilled the dowel post hole. I was originally going to glue it into place but it is so tight I can't remove it without pliers.

    I ended up making one out of steel with a plate on top and bottom and using a steel pin that was removable from the top. You may not have the means to build that out of steel.
    No. I don't unfortunately. I'd offer to buy that if you had it but I'd still have to solve for the level of my baseplate

    Here is something I did before I scrapped using PVC all together. When you move the pvc to drill the next hole and place it on the dowel, place it on the dowel and rotate it clockwise for one hole then the next hole counter clockwise. This is moving the hole tight to one side then the other as there is play in your dowel to pvc fit. This will "alternate" them back and for a little bit, that won't be noticeable and keep it from spiraling around the pipe.
    I like this idea. I had also considered using a laser beam and drawing a line down the middle of the PVC and just methodically making sure the bit is coming into contact with that predrawn line, but I imagine getting an 8' piece to lay consistently straight would be tricky without building an 8' long jig.

    I used a regular drill bit but you have to file/grind the edge of the flute so it is not too sharp otherwise when it goes through the pvc it will grab the pvc and it will shatter. Happened to me and grinding the bit fixed that issue.
    So don't use the forstner or the tapered bits everyone seems to be posting? It makes real clean holes in my 5/8" J Channel.



    Quote Originally Posted by Aurbo99 View Post
    remember that the alignment dowel MUST be tall enough to go through both holes you drill in the pvc pipe to maintain the vertical alignment or you will still get a spiral twist when drilling subsequent holes
    ^ This is a great point. I think I let the dowel get a little low to give me more room to lift and rotate between holes. I could have been at least 1/8" taller or more.

  11. #9
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    Default Re: Struggling with spiraling holes using PVC Jig & Forstner bit

    I posted in another thread that I had the same problem drilling conduit a year ago, completely destroying 20 lengths in the process, the holes rotated about 30 Deg along the length. I used the setup shown in the pictures below, firstly by drawing a center line along each length for confidence, then, using a step drill, and drilling from both sides of the conduit as shown on some You Tube clips. The trick that solved the problem completely was to use a telltale piece of rod through the first or second hole once it was clear of the drilling jig to visually check that the setup is perfectly upright before drilling each hole.

    I have recently drilled 35 lengths of conduit without any issue, 4 x lengths on one hole center spacing, then the rest with a wider spacing. The jig is made of timber and MDF with a steel peg inserted to use for location, I rounded the top to make it easier to get the tube over it. When using a 12mm step drill, the holes were too small to get the drilled hole in the tube over the peg, so I turned the peg down about 0.5mm and had to be very careful about the rotation as there was a tiny bit of rotation available due to the turned down peg.

    One issue I had was getting the peg exactly in the middle of the jig, hence the visible shimming of the side cheeks of the jig to ensure it was central because if the hole is off-center it makes it very difficult to get the pipe over the peg when it is rotated to drill from the opposite side.

    2,000 hole later all good, well actually 4,000 as I drilled from both sides for each through hole :-)

    For some reason the pictures would not load, so check here for them:-

    https://diychristmas.org/vb1/showthr...720#post100720

    Terry
    Last edited by T.D.Sutton; 09-02-2018 at 04:19 AM.
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