lamination grinder

[Gringa Bows]

after reading Gilnockies thread on his lam.grinder i thought i would have a go at making one.

this is how i adjust it up and down for different thickness lam.

the next two are of the hinge set up and it works good.


tomorrow i'm going to try to make a master taper and see how it goes......Rod

[greybeard]

Rod,

You have been a busy boy. The unit looks quite robust.

Have you got side guides for the adjustable bed to get a straight feed and to help stop the lamination from wandering?

Daryl.

[dawallace45]

Rod

Love your new grinder , think I'll make one up for my self

David

[Gringa Bows]

Daryl,ahhhh no i didn't put sides on the adjustable bed but i will today thanks mate, it's pretty strong and i can move it to where i want to work with it thanks Dave,it was simple enough to do,but last week it felt like it was about 50deg.in the sheds ...Rod

[Graeme K]

Hi Rod

When you grind you first lam -- it can be parallel -- you need to measure it at both edges with a vernier to see if it is flat or not -- you then pack the grinder where it bolts to the bench to change the angle and get it to grind flat.

If the lams are thicker one side than the other the limbs tend to twist.

Graeme

[Gringa Bows]

gidday Graeme,thanks for your help i will check that today and have a tinker ........Rod

[Gringa Bows]

Daryl should i put side guards both sides or just one and will i make them say 5or10mill high thanks mate...............Graeme how close to perfectly flat do the lams.have to be does a few thou difference matter....thanks.....................Rod

[Steven J]

Rod,

Nice job.

Just a thought about thickness variation across the lamination. Where a couple of laminations are being used, you could always flip one set to ensure that the low edge on one lamination corresponds to the high edge of the other lamination. This is obviously not the ideal set up (nor the one that would bring the most personal satisfaction) but a solution to a problem non the less.

Don't forget also that when you take your 40mm lam for a longbow down to width in the layed up bow you probably loose 10mm overall (4 thou becomes 3 thou) at the fades and in the range of 30mm (4 thou becomes 1 thou) at the tips. This reduces the variability in thickness in the 'used part' of the lamination also.

Still, I figure it is always best to strive for perfect. I would be happy with +/- 2 thou.

Have fun and don't forget the lung protection.

Steve

[Gringa Bows]

thanks for your help Steve i'll keep playing with it and get it close to spot on as i can...Rod

[Graeme K]

A couple of thou side to side will be fine . ---GKL

[Steven J]

Graeme,

You can probably tell that I am procrastinating today I must have spent at least 15mins thinking that one through.

Steve

[Graeme K]

Hey Steven -- These days it takes me all day to do what I used to be able to do all day -- GKL

[gilnockie]

In order to grind lams from timber, bamboo or whatever, the grinder and the ramp need to be as free from vibration as possible. If there is any vibration the lam will bounce as it is fed into the gap between the sanding belt and the ramp. This is called 'chatter' and it will result in lams where the sanded surface is not flat. It will have high and low spots.

To achieve minimal vibration the the frame must be rigid and stable. It must make uniform contact with the ground or floor so that it does not wobble, the ramp must not bend, it must not move from side to side, it must be kept under mild tension, it must be locked in position so that the gap does not vary, the top of the frame must be absolutely flat and totally rigid and the grinder must be securely anchored to the top.

If you look at the photos of my grinder you will notice that the frame is fairly small, it is made of 75 X 30 mm pine and it is held together with pairs of roofing screws and construction adhesive. Without the sides, it was rigid enough to do the job. I fixed the sides (13mm chipboard) to the frame with construction adhesive and self drilling screws. This prevented any shear in the frame. It also added weight which in turn made it stable. The top of my frame is three layers of 13mm chipboard glued and screwed together.

You also need a digital caliper, a dial caliper or a micrometer to measure the thickness of the lams. You should be able to buy a digital caliper from Bunnings for about $49.95.

When you have produced a stable and rigid frame on which to mount the bench grinder and multitool then you can look at adjusting the thickness of the lam. If your frame and top are flat and rigid, the adjustment should be minimal. If there is any flexibility or movement in the top, you will not achieve a consistent thickness and it can take hours of fruitless effort trying to adjust the multitool.

You adjust the thickness in two stages. First, use the three bolts which fix the multitool to the adapter plate to change the angle of the multitool relative to the bench grinder. I left the flat plate off driving drum because in order to do this I had to remove the lock nut and the washer quite often. The three bolts which attach the multitool to the adapter plate enable about 1 to 2 mm of adjustment. You adjust the three bolts so that the angle visibly changes. If there is not sufficient adjustment in the adapter plate, then you pack one side of the bench grinder to change the angle of the belt relative to the ramp. You then use the three bolts again.

You have to test the gap by grinding a lam every time you make an adjustment. So you will need some strips of timber to test the grinder. I strongly suggest that the side which slides against the ramp has been mechanically planed.

You will need to learn how much clearance is required to grind the lam effectively. I adjust the gap so that the belt rests on the lam and if I can move the sanding belt easily using the lam, that is sufficient clearance. When I grind a lam, I reducethe gap several times, measuring the thickness as I go. I do not try to set the gap to the required thickness before I start.

You will need to learn how to move the lam through the gap between the belt and the ramp at a constant speed. If you reduce the speed at which the lam moves through the gap, the belt will grind a depression in your lam and the thickness will not be consistent.

When you have done all this, then you can begin to test the thickness of the lams. I was able to adjust my grinder so that the thickness of lams varies by no more than 0.02mm across the lam at 6" intervals along the lam.

One final note. If you use sanding belts which are commonly available in your local hardware store, the chances are that the join is formed by overlapping the belt and gluing the two pieces together.This will produce a lam which is lop-sided. The belt which came with my multitool was butt joined with a piece of fibre reinforced tape. This belt does not have any high spots and is the best type to use.

[Gringa Bows]

thanks for your help Norman,i have'nt done much to it in the last couple of days its been too hot ,maybe tomorrow,i'll have to read what you wrote a couple of times to get it to sink in ..........Rod

[Gringa Bows]

Norman,there was a bit of flex in the 12mm.ply so i glued a 20mm.onto it seems to be rigid now,and i bought a digital caliper today so i can try to get the tapers right...........Rod

[Gringa Bows]

i noticed the little wheel with the rubber tyre on the multitool is slightly egg shaped ,are they all like this or is it just mine and will it make any difference to the lams.that i do.i've done a couple of parallel lams.to check with the calipers they seem ok.......Rod