Limb alignment ............

[BigBiker]

Hi

Using a long rod to ascertain the centre line. Is this a good engineering principle?? I know my riser manual states that you should sight the centre of the bow by aligning the front and back edges of the sight window, which seems sensible to me.

Thanks

[pHz]

its fine to use the longrod

but

first check the longrod is straight by holding something straight (i use an arrow) against the sight window and checking it thats parallel with the longrod - if it is then using the longrod is OK - if its not then you have to take note of the angle at which your longrod is out by and compensate for that when checking alignment

(IIRC this is the method outlined by simon needham)

slainte rob

[WhitehartFB]

The most important bit is to make sure the limb tips are straight and the string runs down the centre of each limb.

Most risers are not 100% straight even more so on less expensive handles, so getting the string to run down the centre of the riser is desirable but not always possible.

[geoffretired]

I think limb alignment is about having both limbs pointing away from each other by 180 degrees. That would mean, a line drawn down the middle of each limb, would appear in line with one another when viewed from behind the string line. The centre line does not need to be drawn,as viewing from directly behind the string means the string appears as a line on the limbs and should be seen as passing through the middle of both limbs, end to end.
Using the long rod can be a bit variable, especially if you tighten it different amounts and get different alignments as a result.

[buzz lite beer]

having spoke previously to the tool makers in the engineering shop at work in regard to your question they say the chances of getting a mass produced item like a bow riser to have the long rod bushing or any threaded coupling at exactly 90 degrees to the limb pockets is improbable and not to be relied upon for alignment best stick to usual alignment procedures and if the long rod doesn't lie centrally to your satisfaction after doing so you can pack out one side under the v-bar to re-align

[WhitehartFB]

Originally Posted by buzz lite beer

having spoke previously to the tool makers in the engineering shop at work in regard to your question they say the chances of getting a mass produced item like a bow riser to have the long rod bushing or any threaded coupling at exactly 90 degrees to the limb pockets is improbable and not to be relied upon for alignment best stick to usual alignment procedures and if the long rod doesn't lie centrally to your satisfaction after doing so you can pack out one side under the v-bar to re-align

Likewise a machined/cast riser at any price break, so I do not understand how any line or reference point on a riser can be used accurately as a guide for setting up the limbs especially the tips to be straight. In it's basic form all the riser is the stiff bit of material that holds two springs together and as long as the limb tips are pointing in the same direction and the string runs down the centre of each, the bow will be accurate as the string touches no other part of the bow and the arrow touches the string and the rest/button. I have seen too many bows where the string runs down the centre of the handle and most of the limb including most of the string grove, yet the tips are out of line, which at best means the bow is not as accurate as it should be and worst puts a permanent twist in both or one of the limbs.

[babylon5]

Originally Posted by pHz

its fine to use the longrod

but

first check the longrod is straight by holding something straight (i use an arrow) against the sight window and checking it thats parallel with the longrod - if it is then using the longrod is OK - if its not then you have to take note of the angle at which your longrod is out by and compensate for that when checking alignment

(IIRC this is the method outlined by simon needham)

slainte rob

Rob,

That's pretty much it, as demonstrated on his video and in his book.

[Cimbian]

IMHO the process is flawed from the outset.

Relying on a bushing to be fitted dead square and the thread in the bushing to be dead square and the ferule on the long rod to be dead square to the long rod is highly optomistic.

Everytime another machining process is added and another mass produced part is included tolerances come into play. If you are very, very lucky they will null each other out but this is very unliklely, they are more likely to contribute to a larger run-out... and the longer the long-rod the more this is going to manifest itself.

Even if the holes were drilled, bushed and broached I would not trust this over the 36" of a long rod.

Just think about it for a moment.

[darthTer]

Originally Posted by pHz

its fine to use the longrod

but

first check the longrod is straight by holding something straight (i use an arrow) against the sight window and checking it thats parallel with the longrod - if it is then using the longrod is OK - if its not then you have to take note of the angle at which your longrod is out by and compensate for that when checking alignment

(IIRC this is the method outlined by simon needham)

slainte rob

On the Simon Needham DVD, he also uses a piece of card at the far end of the long rod with horizontal gradations so that when using the long rod in combination with an arrow (see above), you can take note of any deviation from true and align the rest from that mark.

An excellent idea which I couldn't be bothered to do.....the alignment on my riser/long rod was close enough for the level that I was tuning too.

[Cimbian]

Originally Posted by sp220

Having said what i said in my earlier post...

I STILL use a longrod to check the alignment

The principle IS still fine, because you are (in nearly all cases) NOT adjusting in the alignment in increments of tenths of a mm. You are, at best adjusting the increments by 1 or 2mm at a time (more on a Hoyt probably). So, even if the rod is out by 1/2 a mill, it wont matter because the incremental adjustment you make is of a much larger range anyway - especially on the Hoyt system with the washers...

The way to do it is just to use a shorter rod (24"-26") if you have one (which will probably show up as straight). And dont put on the full set of stabilizers untill you have set up the alignment.

You WONT get the alignment perfect - most bows dont come with a system where the alignment can be adjusted in fine enough increments to allow it.

Fortunately, you can get it pretty damn close.

Sam

I don't see this in the real world but as you're studying to a much higher level than I shall ever attain perhaps you can explain.

In the real world you wouldn't notice 1/2 a mil, agreed; however, the error is more likely to be 0.5mm or more at the bush-end by the time you see the accumulated tolerances and as most people would not have a short long-rod kicking around for tuning purposes the errors are likely to be noticeable on their 30" 36" or even 42" rods.

Add to this the distance to the limbs and the problem is worsened, is it not?

I work in electronics and manufacturing tooling and the sort of tolerances above are very-much real world in the mechanical assembly.

I have seen bushes in risers that are skew by at least one or two degrees and I have seen them where they are virtually square yet offset by one or two mm between examples of the same model... even at the higher price range.

The consistency in assembly is just not good enough to use as a reference IMHO, of course.