Author Topic: DIY top slide design, max height 40 mm?  (Read 9861 times)

Offline PekkaNF

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DIY top slide design, max height 40 mm?
« on: November 09, 2012, 02:38:58 AM »
Hello,

I have 125 mm center height lathe (CQ9325 10 x 18" 250x450mm), much like this:
http://users.picknowl.com.au/~gloaming_agnet/cq9325rev.html

top slide:
http://users.picknowl.com.au/~gloaming_agnet/cq9325rev-b.html

The original top slide and it's mounting is too weak and I have replaced it with simple mount for QC-tool-post. However top slide has it's uses and I'm thinking of building one, but I never have build such thing and would appreciate some opinion.

I can think three cenarios for top side use:
* Threading (even the original would do)
* Short tappers, like ER collet holders, MT1/2 maybe even #3 and such (the original has very short travel)
* Fine feed, when adjusted into acute angle, but then handles could foul cross slide handles or tail stock

Am I missing here anything really tactical?

I have round GI stock OD115 mm length 190 mm and some shorter/thicker pieces to work with. I think this would allow me build big enough dove tail slide for 85 mm effective movement.

* What mechanism would be good for swivel?
Original is like this: http://users.picknowl.com.au/%7Egloaming_agnet/1254.jpg
Myford M10 type I'm familiar with http://www.lathes.co.uk/myfordml10/img6.gif
Myford 7 type: http://www.lathes.co.uk/myford-ml7/img21.jpg

I don't want to carve too much into original cross slide assembly and I don't have too much headroom there, I'm thinkking very simple bolt down flange structure. Simple structure means that I need to remove bolts to move it extremes, but when I got it was turned most of time to 30 decree mark (half of 60 decree thread flank or a little less with carbide inserts to prevent rubbing on flank).

* Opinion about lead screw?
I'm not completely happy with cross slide "almost" metric lead and 100 division collar. I'm little tempted to replace cross slide screw with 16x4 mm left hand acme screw, which seems to be fairly common size. Although it might be mostly viable only with new cross slide. I can find 14x4 and 12x3 mm screws on catalogs....I'm wondering if I run out of space for 16 mm screw on top slide would it be very confusing to have different lead on top slide and cross slide? Cross slide and top slide leads are all different on all of my three lathes, but is there an instance this actually would be a problem?

I'm not aiming here for absolute accuracy (bit pointless considering rest of the lathe) but more into confort and reliability.

* Opinion about lead screw placement? Usually it's on the middle, but some smaller and clock making lathes tend to have it much offset or even outside of the dove tail slide. This will cause some assymmetric moment, but how much it is of a factor here? I tend to use top slide mainly for finishing cuts.

* Gib strip placement - of cource towards operator side when crank is on the right? Reasoning is that on "normal" orientation forces act more on fixed side and less on the side that has a gib. Am I missing here something?

* Gib type? I don't see many slide locks on top slides, but for me it's a stiff top slide or quick change between tool post that has top slide and another without. Is this a place for standard set screw gib or something more fancy?

Pekka

Offline loply

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Re: DIY top slide design, max height 40 mm?
« Reply #1 on: November 09, 2012, 03:08:47 AM »
Personally I would just use a standard screw point gib, but use lots of screws to get even pressure.

Can't answer most of your other questions but having done it three times now one thing I would recommend is that you take the time to ensure the leadscrew/handle assembly runs on dual thrust bearings (or dual AC if you wish), has a rotating outer sleeve on the handle, and the largest diameter possible for the handle. All of this will amount to a very smooth operation of the handle which allows you to tighten the gib pressure higher for the same amount of handle effort.

Aside from that as a general principle I would make your dovetails as far apart as possible to minimimise the angular rotation caused by a given amount of freeplay, and make the base as wide as possible where it clamps to your cross side to stop it lifting/bending.

Would love to see the result.

Cheers,
Rich

Offline PekkaNF

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Re: DIY top slide design, max height 40 mm?
« Reply #2 on: November 09, 2012, 06:11:50 AM »
Personally I would just use a standard screw point gib, but use lots of screws to get even pressure.
That was on all designns I have been drawing (some might call that design?), but then I startted thinkking of slide lock and I'm having hard time believing that this design and slide lock could me made to work together. Maybe most people will just adjust it a little "tight"?

Can't answer most of your other questions but having done it three times now one thing I would recommend is that you take the time to ensure the leadscrew/handle assembly runs on dual thrust bearings (or dual AC if you wish), has a rotating outer sleeve on the handle, and the largest diameter possible for the handle. All of this will amount to a very smooth operation of the handle which allows you to tighten the gib pressure higher for the same amount of handle effort.
Thank you. Back to back angular contact bearings and adjusted to eliminate play? OD would be impressive. Have to see thrust bearings catalog.

Aside from that as a general principle I would make your dovetails as far apart as possible to minimimise the angular rotation caused by a given amount of freeplay, and make the base as wide as possible where it clamps to your cross side to stop it lifting/bending.

I agree on the wide and stable/flat base, this I found out first hand: Original would protest on partting off and even on normal carbide insert tooling. When replaced with four bolt base partting off has been easy ever since.

But what about narow quide principle? If dove tail guide is long enough and enoung down force width should not have too much influence on tilt?

Would love to see the result.
Me too :lol: I usually get really excited start with big chuks of metal on completely c/k up and then spend ages trying to bodge it. Or design it ad nauseaum and get eventtualy too discouraged to build it. Just saved one 120 mm OD CI offcut from the skip for base....I'm getting feever.

Pekka

Offline BillTodd

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Re: DIY top slide design, max height 40 mm?
« Reply #3 on: November 09, 2012, 07:30:42 AM »
It'd be worth considering a quick retract function as fitted to Hardinge and other tool-room lathes (very useful for threading).

[edit] see - attached diagram

The lead-screw (32) bearings (13&14), dial(17) etc. are mounted in a sliding block (1) . The sliding block moves in the mount (29) that attaches to the top slide . An eccentric lever (4) move the two parts relative to each other thus moving the top-slide by a few millimetres, another eccentric lock screw (27) limits the movement (allows calibration)

Hardinge uses two R6 deep-groove ball races back to back - I used a pair of cheap-ish ones and ground the faces to remove side play ( easier than you think :))

Attached are some other picture that might give you inspiration :)

The HLV-H top-slide is held on by a single eccentric 'bolt'  - works brilliantly

The nuts on cross & top slides have a fairly simple backlash compensation arrangement

Bill
Bill

Offline PekkaNF

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Re: DIY top slide design, max height 40 mm?
« Reply #4 on: November 09, 2012, 08:03:44 AM »
Thank you Bill, you even add more text while I type :lol:

That excentric lock thingy looks very flat and should be easy enough (even for me) to make. That probably saves the day....I was allready into whole lot more difficult parts and fiddly processes.

And that backlash compensator looks fairly straightforward too.

But those rectactable mechanisms always put me off - I'm sure it's purely pchychological. Could it be circumvented with this flip threading tool?

Offline BillTodd

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Re: DIY top slide design, max height 40 mm?
« Reply #5 on: November 09, 2012, 08:15:18 AM »
Quote
Could it be circumvented with this flip threading tool?

Only for external threads ;) (the retract is handy for internal threads and boring op's too)

The older HLV had a simpler co-axial threaded mechanism to retract the slide (works like a second lead screw).
Bill

Offline PekkaNF

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Re: DIY top slide design, max height 40 mm?
« Reply #6 on: November 09, 2012, 08:34:03 AM »
The older HLV had a simpler co-axial threaded mechanism to retract the slide (works like a second lead screw).

That sounds simpler - in priciple. Probably needs pretty good and axially true thread. Do I need to practice some more threading before I jump head first on this one? I tied once to do a "finetune" sort of differential thread, but completely bombed it....needed whole more true form or more play that I was willing to put into it.

Now - only few more little details :lol:

Pekka

Offline Jonny

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Re: DIY top slide design, max height 40 mm?
« Reply #7 on: November 09, 2012, 09:39:02 AM »
Firstly i would track down where the flex is coming from.
It will be in the poor gib strip or flexing at the rotation clamping.

Far better to use the outer cross slide bolting holes spreading the load.
Even better make it fixed as in rigid you can always put the original back on for those once in a blue moon top slide angle jobs.


Offline PekkaNF

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Re: DIY top slide design, max height 40 mm?
« Reply #8 on: November 10, 2012, 05:00:28 AM »
Firstly i would track down where the flex is coming from.
It will be in the poor gib strip or flexing at the rotation clamping.

Far better to use the outer cross slide bolting holes spreading the load.
Even better make it fixed as in rigid you can always put the original back on for those once in a blue moon top slide angle jobs.

I have the original lying on the self and replaced with a solid bloc, bolted down on the cross slide from all four corners.

The original has these probelms:
* Short travel - something like 35 mm useful - fine for threading pretty useles for anything else.
* Bolted down with two bolts only and these are pretty bad
* Rotation mechansim is weak and footing is narrow
* screw is M12 60 decree form....
* Etc.

IMHO original can't be improved enough - only replaced.

Went on a "bolt shop" and asked if they can source me some 12/14/16 mm left hand trapetzoidal nuts and rods. They sais they'll try but they are not happy...

Been browsing all over and paging trough MEW and now I'm in elimination process for all "unnecessary" to leave only strict necessities left.

Pekka

Offline andyf

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Re: DIY top slide design, max height 40 mm?
« Reply #9 on: November 10, 2012, 07:12:14 AM »
Quote
Could it be circumvented with this flip threading tool?

Only for external threads ;) (the retract is handy for internal threads and boring op's too)

The older HLV had a simpler co-axial threaded mechanism to retract the slide (works like a second lead screw).

You can have flip up screwcutting on internal threads:
http://mikesworkshop.weebly.com/internal-swing-toolholder-for-threading.html
Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline BillTodd

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Re: DIY top slide design, max height 40 mm?
« Reply #10 on: November 10, 2012, 07:22:55 AM »
Neat :)

Pity I can't use one on the hardinge (the spindle does not reverse - only the lead screw)


Quote
Could it be circumvented with this flip threading tool?

Only for external threads ;) (the retract is handy for internal threads and boring op's too)

The older HLV had a simpler co-axial threaded mechanism to retract the slide (works like a second lead screw).

You can have flip up screwcutting on internal threads:
http://mikesworkshop.weebly.com/internal-swing-toolholder-for-threading.html
Andy
Bill

Offline PekkaNF

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Re: DIY top slide design, max height 40 mm?
« Reply #11 on: November 10, 2012, 04:09:12 PM »