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  1. #51
    Yup,
    M8 is 1.25 pitch with 6.8 tapping drill.

    7.0 mm will do in a push, that's the usual size for tough stainless.

    Wouldn't have thought Machine Mart did specials like 1.5 pitch.

    The reason it won't thread is probably because it's a crap tap, can you borrow one off someone ?
    John S -

  2. #52
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    The reason it won't thread is probably because it's a crap tap, can you borrow one off someone ?
    A problem I've noticed with cheap tools is they aren't always the size they claim....I remember drilling the last hole in a big expensive job 18mm instead of 17.5mm caused me no end of trouble...New glasses fixed it ;)
    Thanks All, new expensive tap it is then, dont like borrowing tools (sods law it will break) and its not like I'm never going to use it again. The quill must be tougher than I gave it credit. Did a trial run with the 7mm hole in some Al and it worked fine, a bit loose even.

    M8 thread with a 1.5mm pitch?

    I've been tapping a whole heap of holes for my recent CNC build. For an M8 thread with the more common 1.25mm pitch, a 6.8mm hole is the norm (you sure it's a 1.5mm pitch? as this might account for why your tap is getting stuck!)
    Im going to have to take a note pad out to the workshop as it appears my memory is useless.. yeah the tap is 1.25 pitch

    Thanks again and sorry for the duff info

    With the stalemate on the quill I've been looking at the X-Y table, bit concerned with the flex in the 22mm rails and skate bearing arrangement on one side, and then making up some sort of T slot table.

    For 80 I can get a cast iron compound table (not as big as I would have liked) or I can use some of my THK rails, but still need to sort a table.
    Is 8080 extrusion ok for a table if the rails are bolted to it? Still want it to be as cheap as possible but realised that cutting corners still costs in the end.lol

  3. #53
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    Ok feed up with messing around and decided to take the advice of you guys (think it was the 2nd or 3rd post) and buy a compound table...:clap:

    Got this one
    http://www.axminster.co.uk/product-A...able-21825.htm

    Free delivery is a bonus. Bit of work and it it should be ok. T slot tables of the same size where the same price, so at least I will have a decent table. If it works I will have only spent 100 as the drill was free and the other tools are useful for other projects

    Extra long tap and suitable bolt also on order. Hoping it will all be here for the weekend.

  4. #54
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    A problem I've noticed with cheap tools is they aren't always the size they claim....
    Problem solved, new tap cut like a hot knife in butter. Wont be buying any more tools from Machine Mart...........

    Compound table is useable after all lot of rework. (Think it was cast, rough milled and bolted togother)

    The bit I'm struggling with is eliminating backlash in the acme screw. I've Cut a slot and fitted a pinch bolt, but as the screw and thread are so rough the friction caused is not good.

    My question is how critical is it to completly eliminate backlash or is the compensation in Mach able to overcome it?

    I can probably improve the current state (about 2 or 3 deg. as a guess) but will take more time...

    Photos soon If anyone is interested

  5. The bit I'm struggling with is eliminating backlash in the acme screw.
    How about using a Delrin nut instead of the brass(?) one (or a second nut made of delrin to remove backlash)

  6. #56
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    How about using a Delrin nut instead of the brass(?) one (or a second nut made of delrin to remove backlash)
    Cheers. The originals are cast iron, will the delrin be strong enough on their own if I replace them?

    Wheres the best place to get ready made ones? as the thread is imperial (1/10 inch) Or is it still cheaper to buy a tap and make them my self?

  7. I'd guess they'd be strong enough, although wear rate might be high.

    I think one of the guys on the forum has been making and selling them (I don't know whether he has the correct tap for your threads)

    What diameter are the lead-screws?

    Are the nuts cast in place or are they removable?

    Pictures would be good.

  8. #58
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    Ok you'll have to excuse the photos and the state of my workshop. For some reason if i dont use the flash then there not in focus..:cry:

    The screws are 16mm dia. (15.65 on the calipers) and have a 2.54mm lead (imperial 0.1") Cleaned and polished the screw so thats looking better but just noticed the nut has cracked where I have been tighting the pinch bolt, so definetly need a new one, ups.

    The nut on the x axis is removable and the y axis is fixed.

    Ive had a quick look on tinternet and found lots of different ideas but I'd like to know If any one has a tried and tested method, I've fitted bearings to the screw which was a major improvement, so just need to sort out the backlash in the nut..

    Hopefully when its finished it should be a good MILL.....
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  9. #59
    Screws are 5/8" x 10 tpi not metric,
    Unfortunately 5/8" usually comes in 8 tpi.

    Is it definitely an Acme screw or square thread, acme has tapered sides at 29 degrees ?

    Then are they both RH, LH or one of each.
    John S -

  10. #60
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 22 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    Screws are 5/8" x 10 tpi not metric,
    Unfortunately 5/8" usually comes in 8 tpi.

    Is it definitely an Acme screw or square thread, acme has tapered sides at 29 degrees ?

    Then are they both RH, LH or one of each.
    Bugger.. I thouht Acme was square, and trapazoidal had the taper?

    Anyway they are square and both RH, y axis moves correct but the x is opposite to the lathe (clockwise rotation moves it towards you)

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