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just another DIY indenter

Posted: Thu Oct 22, 2015 1:08 pm
by hatti
hi all! :)
Dan,thank you for massive load of valuable information in this forum.

just got my home made indenter to the "kind of works" phase.
and it works surprisingly well.

since i have no means to calibrate a spring,i did use slightly different method of measuring force applied.
it is like this:
ball is pushed against 1 square cm of oil via rod in cylinder,
oil pressure is measured by manometer.
it measures up to 250 kgf/cm^2,so 250 kilos is maximum force i can apply.
force can be applied in very smooth controlled manner.

the whole thing looks like this
Image

the frame is a piece of 41mm hex steel.
i gnawed out middle part of it,making it into a C frame.
Image

some indents in cable sheath lead using 9.5mm ball and 100,200 and 250 kgs.
Image

i will optimize distances later to make thing more compact.

Andris.

Re: just another DIY indenter

Posted: Thu Oct 22, 2015 1:21 pm
by mtngun
Impressive! 8-)

Re: just another DIY indenter

Posted: Fri Oct 23, 2015 2:46 pm
by hatti
hello again,
i did a little testing on various materials and came up to a couple of conclusions.

most important is fact that the friction between obturated delrin seal and cylinder walls is quite considerable,
it takes extra 50...55 kgs to overcome it and to start really compressing the oil.

in fact oil locks itself into cylinder by its own pressure,the manometer indicates approx 50 kg when there is no pressure from outside. :)


testing was done with 9.51mm ball and 100 kgs on the gauge,but when i tried to calculate BHN using 100 kgs in formula,the result seemed all wrong.
but when i added mentioned above 55 kilos,the results seemed much more sensible - 4.75 for pure lead and 36.75 for copper(should be 35).
pure aluminum sheet- 20(should be 15) :(

and a flatbed scanner can be used for measuring the indentations. :)
the max resolution of my scanner is 600 dpi,that seems to be sufficient.
knowing the resolution,all i had to do was to count pixels.
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copper
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pure aluminum
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pure lead
Image

Re: just another DIY indenter

Posted: Fri Oct 23, 2015 4:13 pm
by mtngun
Well, the friction of the delrin seal is not good news, but at least you are aware of it. :?

Maybe try a smaller diameter cylinder (which would require higher pressure and a different pressure gauge) to minimize the effect of the seal friction?

Good thinking on using the flatbed scanner. 8-)

Re: just another DIY indenter

Posted: Wed Nov 11, 2015 2:10 pm
by hatti
hi Dan

since i cannot get rid of that friction caused variable completely,
i guess i will just learn to live with it. :D

by the way, picked your mold from post office yesterday,
must say it is beautiful.

tried to cast some sample bullets,
alloy was not hot enough,but "force feeding" with ladle did help some.

Image

Image

perfectly round bullets at .4307 dia. yay!

Re: just another DIY indenter

Posted: Wed Nov 11, 2015 2:22 pm
by mtngun
Glad the mold arrived safely. I hope the bullet shoots well in your gun. :)