Radius determination

[Guzrik]

I am making jaws for my hydraulic hose press, and need to get the radius.
I tried to mark it with a marker (since I don't have the blue stuff yet), clamp a rod in and tap it in further hoping it marks.

I am close at 64mm, but maybe someone knows a better way?

 

[daleyd]

Can’t see the images so I’m not 100% on what you are trying to do, but measuring the diameter and using a protractor set to 1/2 this value should be pretty accurate

 

[Guzrik]

https://photos.app.goo.gl/EDfHq2EUfiVPbRkT9

The base for the jaws is in a conical bush, and can be at a range of diameters, so measuring diameter is impossible I think.

 

[carbon]

Are you trying to make replacement jaws? Are the originals parallel as difficult to see when they are in the holder

 

[daleyd]

What is it you are making? If it’s a collet type thing does it need to be that accurate, since it will have some range of movement/adjustment anyway?

You could measure at a few points around the outside and take an average of you think it may not be perfectly round

 

[8ob]

There is a minimum diameter for a crushed ferrule on hydraulic fittings, this varies depending on which system (make of fitting/pipe) you are using, as long as the jaws/collets you make can achieve the correct amount of crush before they bottom out all will be ok.

Bob

 

[Guzrik]

Sorry, the jaws consist of a base (with the screw and spring) and five different sets of inner jaws (black) for different diameters tubing. I need another profile for a specific job but would like to measure the radius of the base jaw segments.
If it is not clear now I wil stop drinking and try again tommorow.

 

[JEZGUZ]

A set of radius gauges should give you the measurement I would think.

 

[Pigeon_Droppings2]

Reckon if you measure one of the segments you might be able to work it out with a bit of maths?

 

[Guzrik]

Reckon if you measure one of the segments you might be able to work it out with a bit of maths?

I like this, unfortunately I am no good in math, but I can sketch it in Inventor tommorow. Thanks.

 

[Pigeon_Droppings2]

I reckon if you measure an individual segment we can have a go on here .

I think we would need a measure of the outer circumference of a segment...and also the length of the sides.

 

[8ob]

I reckon if you measure an individual segment we can have a go on here .

I think we would need a measure of the outer circumference of a segment...and also the length of the sides.

Yep, we could ask Trig

Bob

 

[Agroshield]

Your idea with the marker pen is good but you are applying it to the wrong part. Put it generously on the bit you are poking in the hole and do an in-out motion (no rotation). If the poking-in thing is too small, it will touch in one place, in the middle of a jaw segment. It if it too big, it will touch in two places, at the edges of the jaw segment. When the brass rubbing shows a uniform pattern the width of the segment, the radius/diameter is correct.

 

[nickk]

Yep, we could ask Trig

Bob

Ahh,that will beMr onometry to you then.

 

[voipio]

If the jaw bases are pushed all the way in so they are closed up, does the inside radius seem to flow smoothly from one segment to the next, or does it appear to be "scalloped"? If the former, then measure the diameter of the closed jaw bases with an inside diameter measurement.

Alternatively, this might work, if the measurement contact points are close enough:

 

[Pigeon_Droppings2]

Somewhere there needs to be an allowance for the material removed when the segments are cut....or are you drilling the segments after they are cut?

 

[Pete.]

I would use a cruder method but one that will work when you're lacking actual design info.

Remove one of the jaws from the chuck and mark it up with black pen just as you have done. Turn a disc of steel in your lathe to slightly larger than what you think the radius is. Make the periphery of the disc as thin as you can whilst still being able to reliably measure the OD. Now just keep turning the disc down tiny amounts and use the edge to scrape away the marker pen. At first you'll see daylight in the gap but as you approach size it'll start scraping the marker off at the edges and as you get closer to size very quickly move towards the centre. When the marker pen is being scraped off full width you're at your radius.

 

[Guzrik]

Thanks for all your reactions, I am within a few mm of the correct radius already which might be good enough, but I am looking for a method to determine more accurate if possible without too much hassle.

I reckon if you measure an individual segment we can have a go on here .

I think we would need a measure of the outer circumference of a segment...and also the length of the sides.

Meanwhile I tried Inventor but since the existing innerjaws are cut from one piece and vary in with this is not accurate, also they are made same way as I planned to do; a bush cut it up in 8 pieces with a saw so the pieces of the pie are not 100% symmetric.
These small anomalies, result in mm difference in radius.

Your idea with the marker pen is good but you are applying it to the wrong part. Put it generously on the bit you are poking in the hole and do an in-out motion (no rotation). If the poking-in thing is too small, it will touch in one place, in the middle of a jaw segment. It if it too big, it will touch in two places, at the edges of the jaw segment. When the brass rubbing shows a uniform pattern the width of the segment, the radius/diameter is correct.

I tried this by clamping the piece gently and tap it in further with a piece of brass, this didn't give a clear picture.
Then I tried to slide the rod in and out and that seems to works, my radius is still too big, also see the bottom of this reply.

If the jaw bases are pushed all the way in so they are closed up, does the inside radius seem to flow smoothly from one segment to the next, or does it appear to be "scalloped"? If the former, then measure the diameter of the closed jaw bases with an inside diameter measurement.

Alternatively, this might work, if the measurement contact points are close enough:

I migth still try this since I have a very acurate (0.001mm) analogue measuring gauge (clock?), so if I do the calculations in Inventor this might work. Do need to fabricate the block with the to pins.
The length of arc I have is only 22mm so I wonder if this will give accurate results?

Somewhere there needs to be an allowance for the material removed when the segments are cut....or are you drilling the segments after they are cut?

No the segments don't need to have a nice constant radius when fully closed, all the original ones are also just cut from one bush.

I would use a cruder method but one that will work when you're lacking actual design info.

Remove one of the jaws from the chuck and mark it up with black pen just as you have done. Turn a disc of steel in your lathe to slightly larger than what you think the radius is. Make the periphery of the disc as thin as you can whilst still being able to reliably measure the OD. Now just keep turning the disc down tiny amounts and use the edge to scrape away the marker pen. At first you'll see daylight in the gap but as you approach size it'll start scraping the marker off at the edges and as you get closer to size very quickly move towards the centre. When the marker pen is being scraped off full width you're at your radius.

I was doing this with the piece (34CrNi) itself and it works somewhat.
But it is better and easier to make an aluminium disc and cut it down in 0.5 mm steps, so I don't cut my piece too small.
Think instead of removing I will open them to the maximum and have enough space.
I am now at 64mm so I expect 2,5" (63,5mm) will be the radius.
Thanks everyone, I will report back.

 

[Pigeon_Droppings2]

If the segments are irreleguar you just have to measure each of them. It's the outer circumference that you need....then measure inwards to the radius you want. Sounds very clear...in my head....probably not so much written down.

 

[RichardM]

How do they work? Take the diameter a of the outer they are held in and deduct twice the height of one segment b .