What is the best medium for making a witness mark?

[Doyle]

I need to determine where one surface is just barely bumping another surface. If they were going to make solid contact, an ordinary felt tip marker would do the trick. However, the bump isn't causing enough friction to wear off the marker. I need a marking medium that is more delicate than felt tip or one that transfers readily from one surface to the other. Needless to say, whatever material used must also be safe inside a firearm action.

Recommendations would be appreciated.

[FrankenMauser]

Grease.

[Nodak1858]

Wife's lipstick

[cptjack]

Cole chisel

[HiBC]

The stuff made to do the job is called Prussian Blue.
Dykem Hi-Spot is one brand.

I have used it a lot,I don't know of anything near as good.

Sometimes a local auto parts store will have it.I thinkPerma Tex makes a version. You can get it from Amazon or e-bay,Fastenal,Graingers..MSC,etc

http://itwprofessionalbrands.com/144...m-hi-spot-blue

[Doyle]

That Dykem stuff looks perfect, but I since I need it for only one job spending $10 for a tube isn't ideal. Unfortunately, I don't have any friends who are machinists. I might try Nodak's idea first. My wife doesn't wear bright lipstick but I'll check and see if my daughter has any of the super-bright stuff laying around from her dating days.

[Unclenick]

Hi Spot Blue or Prussian Blue in a grease base work fine. But if your surfaces are conductive and not in contact until you make them "kiss", then an ohmmeter with a continuity buzzer is the easiest way to discern initial contact.

If there is metal-on-metal contact before the surfaces you are interested in kiss, such as threads bringing the surfaces together, the inexpensive way to work is to smoke one surface with the yellow flame of a candle or a match. The soot comes off very easily and works well to detect contact.

[FITASC]

Lamp black is what the British best gun makers use.

[HiBC]

Lamp black is what the British best gun makers use.

I agree hat is another good choice. You just need your vintage carbide miners lamp commonly in the shooter's kit for blackening sights.

Or a candle

[log man]

Smoke it with a wax candle.

LOG

[T. O'Heir]

"...is called Prussian Blue..." And that's ink. Also called layout dye. A Sharpie works as well.

[HiBC]

"...is called Prussian Blue..." And that's ink. Also called layout dye. A Sharpie works as well.

No. Wrong information.Folks are going to spend money on the wrong products.

Dykem is a brand.They make more than one product.

Layout ink comes in blue or red.It gets sprayed or brushed on stock and is allowed to dry.It provides for clean,precise scribe lines when making a layout for machining.

Hi-Spot or Prussian blue is a thin grease like transfer ink that is non-drying.

It is useful for checking kiss-offs and shutoffs in mold and die work. It is useful for inletting and hard fitting.

If you look up "Hand scraping ways" on you tube you can see how it is used with precision flats to scrape in machine ways.

https://youtu.be/k4lUmE945js

Very useful stuff to those with skills.

And,as usual,those who pretend to have knowledge or skills they lack can put out misleading information as fact.

I actually have experience using both products.

[dahermit]

"...is called Prussian Blue..." And that's ink. Also called layout dye. A Sharpie works as well.

It as T O'Heir says, is "layout dye." I comes in several colors besides Blue. I keep both Red and Blue layout die on hand. The some of the other machinistes in the tool room in which I worked would just use a Black marker. However, I like the texture of the layout dye for layout and marking because it would rub-off easier when mating two surfaces exposing the high spots/contact points.
Note: Another substance known as "Prussian Blue" comes in tubes for painters is sometimes mixed with petroleum jelly and used for inletting rifle stocks.

[LineStretcher]

Dykem Steel Blue Layout Fluid. Dries in minutes. Don't need to be a machinist if you have Google. O.K. I cheated, I took metal shop in the 8th grade so I already knew what it was. As a side note I graduated high school in 1971.

[HiBC]

You can use a sharpy or layout ink (or copper sulphate solution,or cold blue) to see what "scrapes off". Thats useful,too.

Its a good trick. But the(layout fluid) product's intended use is painting stock for layout lines,which might be done with a surface plate and height gauge or a rule,scribe and square.It provides nice contrast and sharp lines.

The Hi-spot needs no vaseline,its perfect out of the tube. A pipe cleaner is not a bad smear tool for small areas.Its not a dry product,but in use functions like the old blue carbon paper.It tells you where two surfaces contact.

Then you know where to scrape.The high spots.

Yes,old school shop lost arts.

[HiBC]

Some molds are a simple A side and B side,two halves just open up. There might be through holes,created by core pins that just touch off. A little prussian blue checks the shutoff.

Molds have ejector pins.You don't want those contacting molding surfaces on the opposite side.So the ejector pins are mounted in a return plate,driven back into place by return pins.Return pins need to be flush with the parting line.

What if we are molding a pipe tee or other side action part? We have slides that may travel at 90 deg to the parting line,moved by cam pins that may best at 15 deg,,but they won't hold 15,000 psi injection pressure,so a heel block set into the plates at 18 deg accelerates and locks the slide.The slide has to close and clamp at the same time all the cores and the parting line does.

Since flash in unacceptable in quality molded parts,and its hard on tooling..

And since many plastics flash at clearances over .0004 to maybe .0007 in,

A whole lot of steel plates,inserts,cores,pins and slides all have to be fitted and timed just right.

I'd mostly get it just right with measurements,but these molds represent weeks of work for one man,are worth between $20,000 and $50,000 apiece,and many of the tolerances are less than .001.

And there is a deadline of having product ready to stock on the retailers shelf.

The "B"side of a mold is typically3 or 4 plates laminated together.Most of mine clamped with 40 tons pressure.

So its a real good idea to do a mockup mold assembly using Prussian Blue to verify shutoffs,parting lines,etc.

I use prussian blue a lot building a 1911. You really know how the barrel lugs fit the slide,for example.

[4V50 Gary]

Even if you don't have carbide, soot from a candle has been used a long time.