# How is this possible.



## Corrado (May 18, 2021)

Yes....how is this possible?
I have a 4 year old Optimum BF20L Milling Machine with DRO fitted. (Photo attached)
When I set up a job to be milled in the centre of the work such as steam engine ports I will use the DRO with the edge finder ....locate the exact edge  & move into the centre of the work with the DRO & mill away.
The problem is that when I use this method for drilling holes it is spot on accurate.......however when I attach the Milling arbor (ER 32) it is .5 mm out on the X axis!!!!
I originally thought I was setting up wrong and have rechecked everything over & over. I have rechecked the diameter of the Edge Finder shank..all ok.
Then when I put the drill chuck back in place...everything is spot on again.  What the F##K!
Has anyone here come across this issue?


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## kadora (May 18, 2021)

I have the same bf 20 mill and had the same problem then I found Z axis was not perfectly perpendicular to the mill table.so different lenghts of chuck and ER arbor did this problem.


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## SmithDoor (May 18, 2021)

Bad news it nothing new.

Dave 




Corrado said:


> Yes....how is this possible?
> I have a 4 year old Optimum BF20L Milling Machine with DRO fitted. (Photo attached)
> When I set up a job to be milled in the centre of the work such as steam engine ports I will use the DRO with the edge finder ....locate the exact edge  & move into the centre of the work with the DRO & mill away.
> The problem is that when I use this method for drilling holes it is spot on accurate.......however when I attach the Milling arbor (ER 32) it is .5 mm out on the X axis!!!!
> ...


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## Corrado (May 18, 2021)

kadora said:


> I have the same bf 20 mill and had the same problem then I found Z axis was not perfectly perpendicular to the mill table.so different lenghts of chuck and ER arbor did this problem.


Hi Kadora,
Did truing up the Z axis resolve the issue?


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## Chiptosser (May 18, 2021)

Have you put a travel indicator in the spindle and trammed the head?
Swing the spindle 360 degrees on the table.


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## kadora (May 18, 2021)

truing Z axis help me a lot . But I think that tuning Z angle is quite delicate operation because Z angle setting is not solid enough on this mill. I have to check Z angle quite often.
In spite of this I am happy with this mill.


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## SmithDoor (May 18, 2021)

I use good old dial indicator. 
It works ever time.

Dave 



kadora said:


> truing Z axis help me a lot . But I think that tuning Z angle is quite delicate operation because Z angle setting is not solid enough on this mill. I have to check Z angle quite often.
> In spite of this I am happy with this mill.


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## Corrado (May 19, 2021)

Chiptosser said:


> Have you put a travel indicator in the spindle and trammed the head?
> Swing the spindle 360 degrees on the table.


Chiptosser....you are 100% right.
I Trammed the Head/Table & it was 5.0...yes 5.0 mm out!!


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## BaronJ (May 19, 2021)

Hi Corrado, Guys,

I also have a BF20LB clone and have made some mods to it which improves it tremendously !






One of the first things that I did was to make this tool.  As you can see here the tram is within 1 thou.

Note: that the tram does vary as you move the head up and down ! But that is mainly due to the rather horrible banana shaped gib strip.  Flattening that gib strip out and replacing both locking pins (the ones under the locking screws)  removed most of that variation.






I also did the three bolt modification.  This not only makes it easier to tram the head but also makes locking the head more secure.






Adding an adjusting screw on each side of the head also improves the ability to set and hold the tram.  Once set you can rotate the head and get it back to an almost perfect tram afterwards.






Just in case you don't have the details for the three bolt modification here is the drawing for it.  I just glued it to the head and drilled the three holes.  The bolts were coach bolts with the heads filed so that they fit into the slot without fouling.

Simple changes that make the mill much nicer to use.

HTH.


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## goldstar31 (May 19, 2021)

Hi BaronB
 Thanks for the jolt.
The Multi position Saddle stop HK1840 from Hemingwaykits is here and I'm trying to make the additional is slowly  being attempted. 
Oh dear. the precision with this alnost  non existent eyesight

If I manage , I will have 6 position stops on the Myford


Cheers

N


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## BaronJ (May 19, 2021)

goldstar31 said:


> Hi BaronB
> Thanks for the jolt.
> The Multi position Saddle stop HK1840 from Hemingwaykits is here and I'm trying to make the additional is slowly  being attempted.
> Oh dear. the precision with this alnost  non existent eyesight
> ...



Hi Norman, I've sent you a PM.


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## goldstar31 (May 19, 2021)

BaronJ said:


> Hi Norman, I've sent you a PM.



Many thanks

I hope my reply is Coherent

Keep going

Norman


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## ajoeiam (May 20, 2021)

BaronJ said:


> Hi Corrado, Guys,
> 
> I also have a BF20LB clone and have made some mods to it which improves it tremendously !
> 
> ...




I don't recognize the term 'coach bolts' - - - - - - a pic would be useful.
(Guessing they are what is called carriage head bolts here. (domed top coming to a flat that has a square feature where the shank hits the head. The square is used to give a locking feature in the tightening of the nut on the threads.) 

English speakers are "often divided by the use of a common language"  .


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## IanN (May 20, 2021)

ajoeiam said:


> I don't recognize the term 'coach bolts' - - - - - - a pic would be useful.
> (Guessing they are what is called carriage head bolts here. (domed top coming to a flat that has a square feature where the shank hits the head. The square is used to give a locking feature in the tightening of the nut on the threads.)
> 
> English speakers are "often divided by the use of a common language"  .



Hi ajoeiam,

You are right - what you call a “carriage bolt” we call a “coach bolt”

All the best,
Ian


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## BaronJ (May 20, 2021)

Hi Guys,

Thanks Ian !  

Yes !  If you look at the picture carefully you can just make out the flats below the head.


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## ajoeiam (May 21, 2021)

IanN said:


> Hi ajoeiam,
> 
> You are right - what you call a “carriage bolt” we call a “coach bolt”
> 
> ...


Thank you for confirming my 'guess'. 

Hopefully not sounding like an idjiot but the most common such on this side of the water are rated at only a 36k psi yield strength. 
Grade 5 and 8 are supposedly available but in quite a few years of 'playing' with these suckers I've only run into some that look forged and seem to be mostly for railroad (I think) use that are stouter never the grade 5 or 8. 

Mentioning because the shown use is to hold a machine tool head in position - - - - someplace where I don't want movement unless I'm moving it (and having 'enjoyed' watching a 3" square (75 mm) section flange some 12" (300 mm) OD flange come off the piece I was machining missing me by hairs and flying across the shop - - - - I was rather jittery for a few hours after that!).


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## johnwm (May 21, 2021)

In the UK commercial usage the term for this carriage bolt is "Cup and square"


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## BaronJ (May 22, 2021)

ajoeiam said:


> Thank you for confirming my 'guess'.
> 
> Hopefully not sounding like an idjiot but the most common such on this side of the water are rated at only a 36k psi yield strength.
> Grade 5 and 8 are supposedly available but in quite a few years of 'playing' with these suckers I've only run into some that look forged and seem to be mostly for railroad (I think) use that are stouter never the grade 5 or 8.
> ...



Hi Joe, Guys,

The coach bolts are perfectly adequate in this application !  Don't forget that there are four bolts, three M12 and one M14 holding this head in place.  Normally there would only be three.  The issue with three is that the head is pulled when there are only two bolts that are offset from the center.  The extra bolt ensures that the head is pulled square onto the face.


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## goldstar31 (May 22, 2021)

Hi Guys

50 years ago today, I married the 2nd Lady Fellow in dentistry at the Royal college of Surgeons at bEdinburgh.  She had spent from 1956 learing to drill and fill holes and would continue to do it until she was too expensive and  learned to plsay the barisaxophone and  create yet another little one who would follow her Mum- and would do it on Ilkley Moor B'aht  Hat.

I\ve digresses but  one of our members has summarised it all into  6 lines writte in bad Engllish of how he  drilled holes

Sorry but - Xoach bolts!!!!!  @3ll, they  are no diffrent to carriage bolts. I could never differentiate when it was a coach and when it was a carriage but the village blacksmith made them along with nails  right back -- to the Iron Age and no doubt before that.

The heads  were square because saolrs especially were found of showing their brawny muscles-- and       twisted the heads off. Beieve it or believe it not the  Lords of Admiralty  actuall specified just how BIG they bolts should be.
It was much later in the Industrial Revoltion that things were round or hexagon and  made  on the anvil originally with a 'Bob and Aunty'.  Do I have to explain  what Bob and Aunty did when the rest of the family were abed and not watching.

Well that is the vstory.  What went on after the start of many many years has nothing to do with coach bolts


Norman-  now a widower nudging 91 years


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## ShopShoe (May 22, 2021)

FYI: Historical Comment:

Another  piece of information regarding blacksmith forging of carriage bolts is contained in an episode of "The Woodwright's Shop" on American PBS. Season 36, Episode 12, starting about 19:00.

video;_ylt=AwrE19iT9ahgOIIACQ1XNyoA;_ylu=Y29sbwNiZjEEcG9zAzEEdnRpZAMEc2VjA3Nj

What the blacksmith presents in this video seems logical to me as well. Simpler for a smith to do than making a bolt head for a wrench.

--ShopShoe


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## goldstar31 (May 22, 2021)

I apologise as my poor sight is unable for me to enjoy the visdeos.

What we wend to miss out is what the orinnal bolts were made from.
They were actually forged from 'wrought iron' `nd not steel.
My father appears to have been apprecticshipped( Is that a word?) to a coach - proper coach builder from the age of 12 and used to talk about things like lancewood- whatever that that was.  Be that as it may he  was a blacksmith farrier at 17 and after setting fire to an unwilling Army cart horse on the Isle of Anglesey inn North Wales-- land of the Great Telford and bridges, taught  pntoon b ridge building across the Menai Straits. So he sort of dodged a Great War-- but sent others to be killed. Anglesey is where one of the Megalthic Yard thing  preceded- just aboout everything and used the Planet Venus.  I idigress  but there things still in Cumbria called Beehive ovens. 
Of course square studs in wrought iron  were nailed. into keep and castle doors.  It's not new  unless less you regard that great armourer :eoardo Da Vinci is one of the Moderns of the Middle Ages.
You see steel is - as we regard it today- is quite recent. 
Steel was made  by hammering out and folding  orinally castiron, then wrought iron and then adding carbob  like making a Swiss Roll. The story- I've told it before- was German Emigres from Solingen making swords locally here and the steel could be  wound into a gentleman's top hat..
Tempering as far as I can recall wasthe and the tank was urinated- as needs arose.
I was the little virgin lad as decreed to add to the mix but I was not ginger haied and did my best

Norman


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## hopewu (May 30, 2021)

It may be because it has been used for a long time, so the machine will wear out. Some parts will cause a decrease in accuracy due to friction.


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## hopewu (May 30, 2021)

hopewu said:


> It may be because it has been used for a long time, so the machine will wear out. Some parts will cause a decrease in accuracy due to friction.


Btw, my laser engraving which I bought from OMT three years ago, still works well.


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