Alongside Scottish leader Ruth Davidson, Mr Cameron said that together the Labour Party and the Scottish nationalists posed a threat to the UK.
The manifesto was published as the Scottish Lib Dems, the SNP and Scottish Labour continued spreading their campaign messages on the doorsteps.
In front of party activists, Mr Cameron said: "We've got Labour and the SNP on opposite sides - slugging it out - but if you take a step back they're really on the same side.
"You have a weak Labour Party, who want more spending, more borrowing, more debt and more taxes.
"And the people who will prop them up, the SNP - who want even more spending, more borrowing, more debt and more taxes.
"Together, they pose a clear threat to the future of our United Kingdom. A coalition of chaos."
He added that the result would be job losses, massive tax rises and an economy "back on the brink of bankruptcy".
By Brian Taylor, BBC Scotland political editor
David Cameron has repeatedly - and I mean repeatedly - argued that Labour and the SNP are mutually interchangeable; that they favour broadly the same economic approach (a flawed one, according to the PM); and that they would form a pact in the Commons, by dint of enforced arithmetic.
Why make this point so frequently? I discern a dual purpose. In Scotland, the calculation is that folk of a Unionist inclination - whether Tories or not - will respond to the Tories' claim that such a deal would advance the prospect of a second independence referendum. And will vote accordingly.
South of the Border, the calculation is that the good and sensible people of England - or, more precisely, those of a Tory leaning - may be exercised by the prospect that Alex Salmond (and they always cite Mr Salmond, deliberately, as the bogey-man) will have influence over the governance of the UK.
It is, therefore, entirely a negative campaigning tactic. But then who said politics was purely about the positive?
Although Mr Cameron highlighted the prospect of a Labour/SNP coalition, the Labour Party's Ed Miliband has officially ruled out such a move.
However, he has not discounted another type of arrangement, including a possible vote-by-vote deal.
Voters in Scotland join the rest of the UK by going to the polls on 7 May to choose their next MP.
The Conservatives are defending one seat north of the border with polls suggesting the SNP would win the majority of Scotland's 59 Westminster seats.
Nationwide, polling has indicated that no one party will have a clear majority of constituencies, leading to speculation there will be a hung parliament.
At the Emirates Stadium manifesto launch, Mr Cameron also pledged more powers for the Scottish Parliament, but he also defended plans to give MPs from England a veto on English taxation, once Scottish income tax rates and bands are devolved.
Other key priorities in the Scottish Tory manifesto included;
employing 1,000 extra nurses and midwives; expanding the health visitor service and making it easier to see a GP
reforming Scottish education by building a system where every child gets the "best possible start in life and have zero tolerance for failure"
creating 10,000 new apprenticeships every year and taking everyone earning less than £12,500 out of income tax
extending the "help-to-buy" scheme further in Scotland and reintroducing the right to buy socially rented properties and launching a new "step-by-step" scheme to gradually help tenants own their own home
providing free childcare to all two-year-olds from the poorest backgrounds
allowing individuals, parents and charities to set up new schools, similar to free schools in England
raising the 40p income tax threshold to £50,000 and increase the inheritance tax threshold for married couples and civil partners to £1m
and continuing to increase the Basic State Pension by at least 2.5% through the triple lock
Following Mr Cameron's address, Ms Davidson told the Glasgow gathering that Labour's Mr Miliband, his shadow chancellor Ed Balls and the party's Scottish leader Jim Murphy had turned down "chance after chance after chance" to rule out working with the SNP.
She added that the Scottish nationalists would have a "price list and a check list and a shopping list" for supporting Labour in government.
Ms Davidson said; "We know what it is, we know that is reducing our defences, increasing the deficit, increasing borrowing.
"But don't think that snuck in at the end of that shopping list, there won't be more things to bring us closer to the independence we all just voted against.
"That's why we need to point out to the voters of this country that that dodgy deal is being done by the Labour Party and shame on them for doing it."
As SNP leader Nicola Sturgeon prepares for the BBC's election debate later, the party's John Swinney was on the campaign trail.
During a visit to Leith to promote the SNP's jobs plan, he said the Scottish Tory manifesto was "irrelevant".
He told the BBC: "They [Conservative Party] want to cut Scottish MPs out of decision making at Westminster, when issues decided at Westminster are still affecting the people of Scotland.
"And they are pursuing an austerity agenda which is hugely damaging to the people of our country and Scots are facing real hardship as a consequence of austerity. We need a strong group of SNP MPs elected on 7 May to bring that austerity to an end."
'Talking up SNP'
However, Mr Murphy said Mr Cameron was "desperate" for the SNP to beat Labour so that his party would have a chance of clinging on to power.
Speaking from the Scottish Gas training academy where he was visiting apprenticeships, Mr Murphy explained: "In every election, going way back to 1924, the biggest party has gone on to form the government.
"So David Cameron is desperate for the SNP to beat Labour and he's talking up the SNP in the hope that Scots go out and vote for them, to reduce the size of the Labour party in parliament so that he can cling on to power."
Scottish Liberal Democrat, Sir Malcolm Bruce, said the best option for voters was to stick with his party.
He added that the Lib Dems were determined to retain the 11 Scottish constituencies they won at the 2010 General Election.