401 thump

301, 401, plinths and assorted idler stuff
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Greg
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Post by Greg » Wed May 28, 2008 3:28 pm

Gentlemen, certainly Araldite has been used to repair a motorcycle gearbox and at the time was used in the advertising campain to demonstrate how durable the epoxy resin glue was. This was shortly after the glue was first released on the market. I probably shouldn't have used the term 'sprocket'. It was an internal toothed cog that was repaired. From memory, the story was that a motor cyclist was riding miles from civilisation (possibly Africa or Australia) when he suffered a gearbox failure. He stripped the gearbox and found one of the cogs had a couple of teeth broken off. He filled the gap with Araldite and when set, he cut and filed to fashion two new teeth. He then continued his journey for several hundred miles before reaching a dealership. When the gearbox was stripped down to replace the cog, the Araldited repair was found to still be sound with little evidence of wear. Araldite used to show a photo of the repaired cog in their advertising.

Best wishes,

Greg
Last edited by Greg on Wed May 28, 2008 3:49 pm, edited 1 time in total.

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Post by Greg » Wed May 28, 2008 3:47 pm

Hi Gary,

I had a good look at the Garrard I serviced today. As I suspected, there is no adjustment that can be made to the height of the idler wheel. The adjustment I think Andrew refers to is for alignment of the stepped motor spindle drive wheel which has 3 grub screws on a 401 and 4 on a 301. I wonder if the new thrust plate in your bearing has slightly altered the height of the spindle, lifting the platter slightly higher thus causing the idler to ride over the dings when previously it didn't. Whatever the cause, I know my repair suggestion would work on the platter and if it is riding slightly too high, as suggested previously, some thin spacer washers between bearing housing and the chassis may well work well.

Where in the world are you? If you can get to Bristol, I'll happily look at it for you.

Best wishes,

Greg

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Post by Darren » Wed May 28, 2008 3:55 pm

Yes I've used it to repair casings more than once.

It was the "gearbox sprocket" repair that threw me... :D

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Post by garyt » Wed May 28, 2008 7:35 pm

Thanks for the tips guys - I'll pick up some Araldite & emery paper at the weekend & have a go.
Thanks, Gary

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Post by garyt » Fri May 30, 2008 3:38 pm

Applied the Araldite last night, and took the emery cloth block to the platter this afternoon. I got the surface as smooth as possible, and tried it out. It is a lot better - the thump is still there, much reduced so a lot more tolerable. The good news is that Greg's suggestion was successful - I know where the problem lies, so it may mean a few iterations of apply Araldite & rub down before it's totally fixed.
Thanks a lot guys, your help & suggestions have been invaluable, and really show how the net can work to the advantage of all in communities such as this.
Gary

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Post by Andrew » Fri May 30, 2008 4:16 pm


I had a good look at the Garrard I serviced today. As I suspected, there is no adjustment that can be made to the height of the idler wheel. The adjustment I think Andrew refers to is for alignment of the stepped motor spindle drive wheel which has 3 grub screws on a 401 and 4 on a 301.
Yes, Greg, now you come to mention it, you're right, it was the spindle I was thinking of, apologies Gary, if I misled you.

-- Andrew

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Post by garyt » Fri May 30, 2008 4:45 pm

Andrew wrote:

I had a good look at the Garrard I serviced today. As I suspected, there is no adjustment that can be made to the height of the idler wheel. The adjustment I think Andrew refers to is for alignment of the stepped motor spindle drive wheel which has 3 grub screws on a 401 and 4 on a 301.
Yes, Greg, now you come to mention it, you're right, it was the spindle I was thinking of, apologies Gary, if I misled you.

-- Andrew
Yeah, for my issue, it's a pity the spindle can't be fitted 'upside down'. It would mean 33 RPM would be where 78 is at present, and I wouldn't have a problem!
Gary

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Post by Greg » Fri May 30, 2008 8:35 pm

Hi Gary,

OK, good that you are making progress. If you still have a slight thump it will be down to 1) The repair you have done not being sufficiently profiled to replicate original. 2) The damage also includes the rim being out of round. 3) The idler is running too low (or the platter is lifted too high) on the rim.

If the rim of the platter is out of round, the solution will be a new platter or if the damage is outward (if you see what I mean) using Araldite to infil and then rubbing to get a good internal round finish should sort it.

I still think the issue is around where your idler is driving the rim of the platter. I've realised my previous advise has been incorrect because (not thinking through properly) the main bearing housing is fixed from the top of the chassis so there is no way of dropping the height of the platter (only lifting it). If that turn out to be the case you'll need to engage on this with Slatedeck. There is little alternative. Knowing the director and the company I have absolutely no doubt that they will want to resolve this. I hope that helps.

Best wishes,

Greg

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Post by Nick » Fri May 30, 2008 8:49 pm

I don't know if this is practicle (Darren?) but would it be possible to skim the inside face of the platter in a lathe to remove the problem area?
Resistance isn't futile it's V / I.

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Post by Greg » Fri May 30, 2008 9:19 pm

Hi Nick,

Yep, that certainly could be done with Alraldite infill or without. It certainly could be a solution. I still feel there is an issue on the height location of the idler on the platter edge.

Best wishes,

Greg

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Post by Darren » Fri May 30, 2008 10:56 pm

Hi guys,

I've pretty much kept out of this so far.

To bring you up to speed we (Slatedeck) did supply a new thrust bearing.
After this the platter height issue was brought to light. So we double checked the bearing height and it was found to be correct.

If Gary would like to send it back to be I could make absolutely sure before any further measures are taken. I could even skim it down a touch if that would help. But you'd have to make sure the platter has the clearance for this. Usually it's a tight fit in this regard.

Skimming the platter is something I can't do, two reasons. My lathes are not quite big enough to hold the platter, 9" dia max and it would be bloody difficult to center such an object without a lot of hassle.

Then we would have to consider the speed of the platter after it has been skimmed. The more that needs removing the bigger the issue.
A tiny skim off the platter would mean a big change on the motor pulley.
I'd hate to try to work it out, the ratio is huge. But essentially the pulley would need to be bigger.
Be easy if it needed to be smaller, but that's life init.

My view is, a replacement platter is the order of the day. This one sounds too far gone.
Last edited by Darren on Fri May 30, 2008 11:38 pm, edited 1 time in total.

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Post by Darren » Fri May 30, 2008 11:09 pm

Besides, Gary still has the original thrust bearing.

So if he puts that back in then there are no issues that can be connected back to Slatedeck or myself.

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Post by garyt » Fri Aug 22, 2008 5:22 pm

Just an update on this.
I picked up another 401, and tried the platter off that on my current TT. There are no thumps at all, so it's definitely the 'dings' in my original platter that are the culprit. One avenue I had been considering was to fit a rubber seal between the thrust bearing plate & bearing housing - this would have the effect of dropping the platter by the thickness of the seal, as the bearing would sit 'inside' the hole in the middle of the seal (if you know what I mean). I may yet have a go at this, but at present I'm trying to get a new plinth to sit on my Sound Org wall shelf.
Gary

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Post by shane » Fri Aug 22, 2008 7:55 pm

garyt wrote:Just an update on this.
I picked up another 401, and tried the platter off that on my current TT. There are no thumps at all, so it's definitely the 'dings' in my original platter that are the culprit. One avenue I had been considering was to fit a rubber seal between the thrust bearing plate & bearing housing - this would have the effect of dropping the platter by the thickness of the seal, as the bearing would sit 'inside' the hole in the middle of the seal (if you know what I mean). I may yet have a go at this, but at present I'm trying to get a new plinth to sit on my Sound Org wall shelf.
Gary
It might be worth visiting a local engineering shop to get them to skim the inner surface of the platter. No harder than skimming a brake drum, I wouldn't have thought.

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