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BOXFORD IMPERIAL DIAL
micktoon:
Hi Griffin and all, very well explained Griffin and I agree with the Boxford set up it makes sense. I also think it makes perfect sense that the schools and colleges of the time just had to do what they could to get metric without the money to go scrapping dozens of lathes as mills, so overall the plan was ok.
It was bugging me what my dials had been reading on the Harrison but I remembering it was not as simple as mentioned above so I have checked. The dials are metric and I am sure I checked the pitch of the feed screw and it was metric but not 100% about that now time has passed. One full turn of the cross slide dial (graduated and marked 4mm ) is 4mm which is 157.48 thou and the top slide is 2mm which is 78.7 thou.
So am I right in thinking rather than what has been mentioned above my cross slide will have 4x the error per rev and the top slide 2x the error per full turn. Which would mean if I wanted to fit just imperial dials but correct this error I would have to make a cross slide dial with 157 or 158 divisions and a top slide with say 79 divisions ? I think this is why I thought you could not just swap the dial itself for a stock dial designed for the opposite screw pitch, e.g metric to imperial or vise versa ?
I think this is why I thought a DRO seemed like a good idea lol
What do people think , am I loosing the plot or would my options be to make the one off dials as mentioned or get imperial dials and feed screws / nuts.
Cheers Mick
philf:
Mick,
Why on earth would you consider a 157 division dial? You'd still have an error and if you wanted to move the slide say 200 divisions you've got to start subtracting 157.
You have metric dials, metric screws and, I'm sure, a calculator. Stick with metric - it's the future :thumbup:
Is 4mm the actual pitch of the cross slide screw or the reduction in diameter for 1 turn? My Boxford Industrial had 0 to 5 mm on the cross slide dial in 0.02mm divisions with a 2.5mm screw. I prefer the actual movement so I made new dial with 0 - 2.5 with 0.01 divisions. My DRO is set to show diameter.
Cheers.
Phil.
GRIFFIN:
Yeah interesting Mick. I wonder what the graduations are on an imperial Harrison ie how much per full turn?
I'd guess a Harrison would come from a college rather than a school or maybe from industrial use. In either case it would require a more exact solution to the conversion problem and money would have to be spent on a more complete conversion. I'll have to do some more homework and see if there are any Harrison metric conversion kits, etc. mentioned on lathes uk. Certainly the Boxford side of the business was pretty good at using up old stock of imperial parts on metric machines in order to keep costs down.
Just a side note here, the main reason I'm making imperial dials for my Boxford is that I already have a slightly bigger metric gear head Chinese lathe which has a metric thread cutting gearbox and obviously metric dials. Now I have the best of both worlds I can produce metric work on one lathe and imperial on the other without having to use conversion gears every time I go from one to the other. I'm selling my little imperial Warco wm180 as it doesn't have a thread cutting gearbox and it was too much bother changing end gears to do simple threading work. Tee hee, what a lazy b*****d Eh?!!!
:D
Cheers, Griff.
Manxmodder:
Mick/Griff,
The imperial cross slide screw on my Harrison L6 is 10 tpi twin start Acme thread and the vernier wheel has 200 divisions per rev.
Due to the screw being twin start 10 tpi this means the cross slide actually moves 200 thou radial per rev and thus removes 400 thou material cut diametrically.(To take 10 thou off a diameter I have to index in by 5 thou)
This type of screw is commonly fitted to and much more suited to a milling table traverse than a lathe cross slide.
If this screw were replaced with a 10 tpi single start it would then convert the indexing to a more preferable direct diametrical relationship.(10 thou on the dial relates to 10 thou turned off diameter)
My top slide screw is 10 TPI single start and the index wheel has 100 divisions.(100 thou per rev)
I also have a complete set of metric cross slide and top slide screws and index wheels. These are trapezoidal 2mm pitch,though again the cross slide screw is twin lead.
The metric index dials read 4mm per rev for the cross slide and 2mm for the top slide.
.....OZ.
GRIFFIN:
Thanks Oz,
Thought so, no cheap fix on that one. I wonder how much such a conversion kit would cost in comparison to a couple of dials on the Boxford?
Yeh I remember when I first used my second Warco Chinese Lathe, (sorry for the profanity) the previous one had direct diametrical readings so I assumed the second one also did. needless to say that job went in the scrap bin!!!
Cheers, Griff.
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